Well of course they bolt on fine, otherwise there would never be a problem. The mating surfaces behind the accumulator; just in front of the rear band. A 68 won't usually work on a 74. I'm looking for reasons that don't involve removal of the trans. And I never assume anything was assembled correctly before I ended up with it.
I pulled the VB and compared it to the 74 not a spit of difference I can see in the cases. Where and how they mount are both identical. Even behind the accumulator.
Again, I pulled both apart and see nothing out of place or put in backwards.
I’ll be putting the 74 back into the transmission because I believe I can now remove the VB as a variable.... hopefully.