I've been trying to find images of a Cimmaron manual transmission. The only thing I found that I could really make out was a 5-speed. Essentially, it looked the same as our transmissions, but the gear levers were a little different, and it looked like the clutch release arm was down on the side so that it was actually attached to the clutch fork arm. I also did a search for Cimmaron slave cylinders, and the one I found was more on the style of the Getrag, having no mounting studs. It had what appeared to be about a 2 inch pushrod that just barely cleared the dust boot.
I found this on Nemiga.com. It's listed as a 5-speed Isuzu.
https://nemiga.com/cat_spares/epc/cadillac/62j-j/04/mj04-017/And this listed as the M19 4-speed.
https://nemiga.com/cat_spares/epc/cadillac/62j-j/04/gm04-080/Thanks everyone for your input. I'm thinking that they're not a good source of a replacement transmission after all. I was hoping they'd be pretty much a direct swap.