Thanks for the input, guys. I have to admit, I doubt the shim fix as well, but thought I'd ask. I can't see how a .006" shim can make that much of a difference in that location. And, wouldn't it cause an undue amount of stress on the housing when the other bolts are tightened?
Yes, it apparently did pop out on the previous owner but he forgot to mention that.
He did say that the transmission was rebuilt, but who knows how good of a job was done.
I guess I'll start with the shift tower as suggested.