Trans mount idea: I have a poly mount kit that looks like a bunch of washers, poly and steel. I think I inherited it form one of my friends' garage cleanout efforts. It would take some time to find the baggie of parts, but for now, could you fab a 3-hole plate out of some 3/16" stock? IIRC, there is a void in the trans pad above where the bolt head through the Xmem would be. Make a stack of rubber/poly shims and bolt through into the TH400 holes.
Meanwhile, I'll pull out a few drawers in the garage tonight and see if I can find that kit...