shamwow

I have a 1980 chevy vandora with a chevy 350 and matching transmission. The van was converted into a school bus and outfitted with 4wd and I believe given a vin at that time. The 4wd is a unique setup with transfer case acting as front and center differential. two solid axles going separately to each front wheel almost like cv axles but solid, and a third axle going to the rear. transmission is broken and needs replacement. I cant find out how to tell if my transmission is a 4wd or 2wd version. I know the main difference is the output shaft length. Shorter for the 4wd. The first digits of the vin are TGM35A05. The 2nd digit is supposed to be a C or a K for 2wd or 4wd but mine is a G. How can I know which transmission to get?