All Saginaw were coded M20 from memory. M21 and M22 were Muncie in that timeframe. It is only in Australia that we coded Saginaw as M21 and M22, M20 was the Opel shear pin (designed to protect the grey iron banjo!). GMH coded the 2.54:1 box as M21 and the 2.85:1 box as M22. The M21 was used behind V8 and 6cyl but the M22 was only ever used in 6cyl applications, mainly commercials. Although GMH did homologate the M22 for HK GTS327. The gearbox used in GTS350 is the same ratio spec box as all other V8 HK-HG but it was beefed up as the Saginaw was way beyond its design specification behind a 1969 L48 - in a HK sized vehicle the biggest engine fitted with a Saginaw was the L30 275hp 327.
The 3.11 1st gear box was used in the USA in lots of 4cyl and 6cyl applications and possibly optional some small V8 optional applications. Nothing by GMH though.

2.85:1 (M22 in GMH world) was only used in HK-HT 6cyl commercials. There was one exception, and that was in HT GTS if you optioned a heavy duty transmission it was an M22 (in HK it was M21). I guess GMH realised that an M21 behind a 186S in a HK GTS would have been hard on clutches particularly with the standard 3.36 or worse with the economy 3.08 rear axle. The 6cyl HK commercials used an M22 if 4spd optioned but they would also have 3.55 rear axles. So for HT they changed to M22 for the 6cyl GTS model. Although like HK GTS with HD 4spd option, a HT GTS optioned the same would be the rarest GTS driveline option, so rare it might as well never existed.

The M21 Saginaw (only called M21 in Australia, in North America an M21 was a Muncie in the late 60’s) was used in all HK V8 optioned manual vehicles or HT-HG V8 models where 4spd was standard or optioned. There was no other transmission used. As I indicated the FIA paperwork for the GTS327 lists the 2.85:1 box as an alternative transmission, however no production cars would ever have been fitted with one. This was normal practice, the same was done with XU1’s, LH-LX etc, where non-production gearboxes and rear axles were listed as alternatives but never fitted in the VAP’s. GMH Engineering and Harry Firth had access to a few wide ratio Saginaws that they played with in HT/G GTS behind 308’s with moonshot rear axles (like 2.5:1), cars were built but not production vehicles. The diffs were to keep the fragile 308’s well below grenade revs on Conrod Straight and the wide ratio box to get them moving. Those cars were insurance after GMH failed at Bathurst in 1970, and a cheaper alternative to the (canned) earlier Old Man Emu HT GTS350 with its 370hp LT1, Muncie and 12-bolt. Harry didn’t want the 6cyl Torana, he knew you needed a V8 to dominate Bathurst, and he was almost right as the only time a V8 didn’t win from 1967 through to 1987 was in 1972.