[SStockDart]

All of these suggestions sound logical to me.....let me just throw something else out there, in case these suggestions don't fix the problem. I have seen where the back of the blocks were crooked, therefore requiring shims to be sure the bell housing aligns "straight"..
"back in the day", it was common to break 4 speed transmission housings......after dial indicator and shims, I never broke another. Good Luck