..pretty new to buggies - acquired a total of (4) B4.1's or B4.2's

One has mostly new parts, was never finished being assembled....got it all built today, went to run it and there's something not correct in the trans build...no biggie, I grabbed one off one of the other cars...it won't INSTALL

Looking at the rear trans mount, they are different, one appears that the trans sits lower on and I'm guessing there's some slight changes on the trans case. (PULLING HAIR OUT for a 5 minute trans swap...now I have two buggies ALL torn apart and I'm not a happy camper)

Which is which on that rear mounting plate (lower one B4.1 or B4.2?)