I feel like I've done something wrong here. My T-5 trans is 13-52-145 which translates to 85-86 S-10 V6. I tried it in my '54 with the stock bell housing to check the spacing and it bolted right up. I didn't force it, I put the bolts in by hand and just did the last bit with a wrench. I can put it in gear and turn the output shaft by hand. I don't see the need for the adapter plate. Am I missing something here? HELP!!

1954 Chevy custom 261CID, T-5 5 Speed.
1952 Chevy 6400 2 ton hydraulic flat bed.