91 vert, 5 speed, The bolt that connects the tranny support to the frame is stripped. I cannot figure the size, although I could remove the other and take it to the hardware store. However, I was hoping someone would know it.

M8 coarse, x30mm or so.
These strip pretty commonly, lots of different ways to fix it. I tried drilling and tapping it to 7/16" but didn't get enough thread strength out of that "hard as cheese" insert in the frame.

I dropped a socket capscrew in from above.

Search in the trans-driveline forum about tranny cross member bolts or something, that should help you out.

I think actually, they are M10 (15mm head).

hmm, good chance you're right on that. Mine had 3/8" NC, not sure if that was stock for my year, or what the previous-goofball put in there...