Well the trans mount is a new old part I've had laying around forever so I think it's OK and the crossmember is stock but I will definitely keep that in mind.
Re-reading this morning I realized one thing I have failed to do is to loosen the block-to-bracket bolts. I've only been loosening the bottom stud between the mount and the k-frame. That will be the first thing I do the next time I'm at the car.
Based on the 1/8" measurement from yesterday I'm included to agree that the problem seems to be at the transmission end of things.