I had to go on an easter egg hunt recently to get one of my old mills up off the floor and mounted on an engine stand, and for reference in case anybody has lost their original transmission bolts - yes they ARE metric, and here is the benefit of my researches:

M10 -1.50 x 40mm is the original bell housing bolt. (About an inch and a half)

For engine stands with 2 inch spacers, M10 -1.50 x 60mm is a two and a half inch long bolt that fits perfect.

* This size bolt (60mm to 70mm) also works as a replacement for the unthreaded lower engine to transmission bolts, if you get a pair of matching M10 -1.50 nuts. I recommend aircraft type nylon locking nuts

For the NON-threaded holes on an engine stand with 2" stand-offs you need M10-1.50 X 90mm, which is a three and a half inch length that will also need matching M10 -1.50 nuts