we swapped motors, and the 350 won't mate up flush with the t5, there's about a 3/8 inch gap. Y. we've tried everything, so how bad would it be if we just tightened it up? I know it's a big no no with an auto. But what should I do?

 

Find out whats not fitting/binding/stuck.

 

I assume that you mean there is a gap between the bellhousing and trans, right?

I just ran into a similar problem. I swapped the bronze bushing for a roller pilot bearing...and since I didn't know any better...I just pressed the bearing in far enough to be even with the crank.

The solution was to press the bearing further in to the crank and the gap between the trans and bellhousing disappeared.