Limited Production and Racing Models
In Brief:
This section covers the two racing models of the triples and tries to reveal some of the "mystery" versions of the triples.

1971 H2 750 There was apparently a pre-production version of the H2 that was released in Norway and Sweden in late 1971 to iron out problems and see how well it would be accepted. It is not listed in any official literature, and I have no other information on these save for two pictures, one from a brochure, the other from the UK Triples Club Rally. (The rally model has aftermarket pipes and '73 decals on the tank.) Externally it appears identical to the Candy Gold 1972 H2 except for the large "Mach III 750" badge on the sidecovers.

Husson73: On the very first H2 previews in motorcycle magazines, all said carburetors were VM32 but the pictures were so small than you couldn't really know which carbs were fit.  I don't think the press had invented the VM32 and the information about these would have come from mother Kawa: so this could mean some pre serial H2 had VM32 and it would make sense because with the 500 using 28VM you're more expecting VM32 than VM30 unless you wanted  the H2 detuned to avoid the fact the triple would outperform the new Z1 which was supposed coming the year after.

The very, very early H2 - speaking of bikes VIN under 300 or 400- had no trims on the seat, the front mudguard bracket was blue, the front turn signal brackets were chromed, the rear turn signal were H1B, there was a rubber to protect the clutch cable on the clutch perch (look at the brochure), the chain oil tank was round - bikes under VIN 100 or something like this- and fit on the tail rest (if you look at the H2 part list you will see the drawing: round), there were 3 kinds of exhausts, very first had no dents at all for the brake pedals and footpegs both sides just a very small dent for rear pegs, then you had the dent we know for footpegs and brake pedals except the left pipe had also a dent for the gear change, then came the pipes we know for all H2 H2A without speaking about the rear pipe bracket which had variations.

Of course, the H2 until VIN 4400 had the square cutout barrels which had different porting but according to Rick Brett, dyno test weren't more powerful except the power range was different and the engine wilder, earlier carbs were also different with heavy silver slides (look at Kawasaki bulletin), plastic shell front light with special rim, until VIN 2200, rear brake cam or lever longer and brake pedal lever different.
According to Rick Brett there were also 3 types of tacho/speedo colors, green then blue with 2 kinds of blue.  Different tail rests also from the inside.

I don't guarantee the VIN numbers I give just the general idea.
Possibly early S2 rear pegs on the very first and sure on the very first front fork covers were different with no reflector or hole to fit it.
Early frames until VIN 4000 or 5000 had only one tube on the bottom of the cradle (front).

Gold 1972 H2
H2's were made in a Candytone Gold color for the Japanese, Australian, and European markets, even though they were not listed officially in that color. The colors and stripes (red and brown with white) were identical to the 1971 H2 above.
1969/70 Peacock Grey H1 The "Peacock Gray" H1 was a mid-69 model year release of the H1. Most of the '69 models were white, and while Kawasaki lists the grey one as a '69 model, some gray '70 models have shown up. The gray ones incorporated some revisions to the '69 model which were finalized in the red '70 model. Red Introduction
Rick Brett: As far as I am aware ALL bikes KAF06500 (ish) to KAF10000 were grey, KAF10000 to KAF13500 (ish) were mixed Grey and Red and KAF13500 to KAF23000 (ish) were all Red. There are no factory records. VIN stickers began in Oct 1969 with Grey H1.
KH series Not actually a mystery, only worth noting that Kawasaki applied the "KH" code to all their post 1975 two stroke street bikes 125cc and over. So there are KH125's out there, but they're singles, not triples.
H1-C This was a 1972 model H1 (US market only) with '72 colors ("Pearl Candytone Orange"), instruments, and graphics, but still retained the fenders, drum brake, and CDI ignition of the 1971 model. Some sources say the H1-C was an expediency to get rid of stocks of older model parts which the H1-B didn't use. Kawasaki does not list it in their blue 1978 model recognition guide, yet some manuals such as Chilton's mention it.
There does exist a parts list titles "500 1 C" part # 99997-527 dated Oct. 1, 1971 that covers it. The H1 parts microfiche has a section for the H1-C that covers the following frame and engine numbers:

Frame: KAF48664-49664
Engine: KAE043902-045902

From this it could be assumed that 1,000 H1-C's were built.  Later frame numbers thru 52100 and in reality there were approx 1000 units built starting with frame #48664 but ending with #52100 with H1B and H1C numbers co-mingled.

Monotrack SR-1 Monotrack made a custom version of the H1, using racing style bodywork, alloy mag wheels, and a custom electronic ignition. In appearance they resembled contemporary race bikes without a fairing. The models seen in photographs all seemed to use the early '69-'71 H1 motors, although ads claimed H2 motors could be used also. An "SR-2" was also made that used Honda CB series four cylinder motors..
Denco CR-90 Denco made performance upgrades of the H2, and offered porting services and expansion chambers. The "CR-90" was a ported H2 with Denco chambers, 34mm carbs, and various other mods. Price was $2500 in 1975 for a 90 HP. bike that could do the 1/4 mile in 11.48 seconds and top 141 MPH. Only 200 were made for racing homologation rules. (One source quotes 120 H.P. for the CR-90. ?)
(H1-RA, H1-RAS, H1-RS, H1RW)
The H1-R was the production racer version of the H1, available to both private racers and factory teams. A second model, the H1-RA, was made in 1970-71. It used a dry clutch and close ratio transmission, and the original H1-R sold for $1,495 in April, 1970. Authentic racers began with engine #KAE-90001 and frame #KAF-90001.
1970 H1-R Stock inlet (unbridged) four transfers, single oval exhaust port.
1971 H1-RA Bridged inlet, four transfers, single oval exhaust port.
1971/72 H1-RAS Bridged inlet, four transfers, bridged exhaust.
H1-RS No info as yet.
H2-R The H2-R was the production racer version of the H2, available to both private racers and factory teams. It used a dry clutch and close ratio transmission. Authentic racers will have their frame and engine serial numbers begin with 9.
KH-750 Some people have assumed that since Kawasaki made the KH series for all the other models that there was also a KH-750 planned or made in limited numbers. However, it doesn't look like any attempt was made to produce a KH series 750.
KR-750    Hansford The KR-750 was a liquid cooled three cylinder racer, the next logical progression of the H2-R. It was not available to privateers, nor was it made as a streetbike.
"Square Four"
"Steak Tartare"

No. 0280(1)
"Steak Tartare" was the code name (Same vein as "New York Steak" for the Z-1) for a development project at Kawasaki. It was also referred to as the "J-Model" or as project number 0280. It was to be a square four, 750cc, fuel injected liquid cooled two stroke. A combination of increasing noise and pollution laws against two strokes (California at the time threatened to ban two strokes) caused Kawasaki to stop development in favor of the Z-1 in the summer of 1973. 20 examples were built (The surviving one uses carburetors) and they made 70 horsepower and could do 200km/hour. At the same time Yamaha dropped the proposed GL-750, a water cooled inline four two stroke similar to the TZ-750 racer.

(1) Photo of J-Model from the Dutch Triples Club web site.