I'm certainly not an expert on the Thiokol/DMC/LMC line up but my experience is similar to what redsqwrl describes. I bought a 1976 Thiokol 1202C from the LMC sales guy at the time. The data plate said it was a 1202ST which I have seen the ST badge on one other 1200 series but don't know what it means. It had the crew cab, 300 cid ford, c-6 auto, oc-12 rear end with the drop axels, aluminum front wheels and the two piece steel wheels on the other 4 axels, J style track grousers, instruments in front of the driver and a six way blade. Was represented as a one owner machine purchased by Burlington Northern.
My friend had a 1977 Thiokol 1202 that had a wider upper cab, no drop axels and the instruments in the center of the engine cowl but was otherwise the same as mine. Originally owned by Alaska DOT and was sold at auction with the rear end disassembled and needing rebuild. He rebuilt the rear end and it trashed its self right away. He rebuilt the rear end again and sold to a lady and it has sat unused ever since. One of the factory guys I used to talk to said that rear end in that machine had always been a problem or was junk as he put it.
I also had a Thiokol 3700AC hydromaster that was a mid seventies but even the factory wasn't sure exactly when it was built. It had a mixture of small Axel diameter thin webbed aluminum wheels and some thicker large Axel wheels and then some even thicker large Axel aluminum wheels. I bought two new wheels from the LMC factory shortly before they closed the doors and those wheels had very thick webbing and a thickened casting around the bearings.
I have personally seen a few 3700AC, DMC 3700 and one 3700LMC plus many pictures of all the different models and almost all of them have some slight difference among them.
I had parts manuals and quite a few brochures of both 1200s and 3700s and there were many options including engines, axels, rear ends, accessories etc. plus lots of frame and track changes over the years. Very difficult for me to positively identify an exact model at first glance.