differential yoke causes rear trans seal leak?

[mole2000]

I recently had my transmission rebuilt (th400) and the shop said that my rear diff yoke was faulty and needed replacement. They were supposed to fix, but they never got to it. So a week or two later there was a leak so i took it in for them to look at. They said that as the yoke wasn't "correct" that couldn't do anything about the leak, which they said was coming from the rear trans seal.

"Okay, thanks for the help" and I went about my way.

So I got up under there today and pulled the drive shaft looking for something amiss. The rear u-joint fits snugly and securely in the yoke. There is no obvious damage to either the drive shaft or diff yoke. I have not been getting any vibrations while driving.

The truck is a 1970 with a swapped in 454 (unknown year but its HEI) with TH400. It originally came with a straight 6 and column 3 speed. I am presuming that the drive shaft is not original. The differential does appear to be original (based on matching grime/grease anyway)

Multiple questions: Are these 2 things are related? Is the rear diff yoke for a 6 cylinder a different size than for a same year 8 cylinder? Can I pull the rear diff yoke and take to a driveline shop and have the whole thing examined to make sure it matches? I have read that taking the yoke off removes the preload and the whole rear end will have to be set up again.

I'll post some pics in a sec.

Thanks!