So, for an update on this. Had issues trying to get the parts in my town. For now, I've settled for reusing the non-broken thru bolt and starter mounting bolts, and replaced the broken "thru bolt w/extension" with threaded rod for now. Wasn't real happy about this because I wanted to fix it right, but I looked at the way it goes together and I figure it's actually using the tensile strength of the rod to do a lot of the supporting because the bracket is pinched tight against the tailcap by the nut on the stud, and the stud is holding clear through to the nose cone. Decided to use blue loctite on the thru bolts because the red stuff isn't recommended for anything under 3/8".
Got all that ready to go back in, even cleaned up the starter a little bit, and ran into issues trying to get the smaller wire reconnected to the solenoid, lost the lock washer, found a replacement, finally had to take the starter back off of the block to get it done, and got the starter remounted, complete with shim and red loctite on the mounting bolts. Tightened the nut for the support bracket on the stud, and got out the torque wrench....
TMs recommended torque for the mounting bolts and the support-bracket-to-block bolt is 33ft-lbs. Torqued the mounting bolts with no problem. (If you can see the writing on the wall, start shaking your head now.)
Evidently when I got a bolt to fasten the bracket to the block before, I asked the guy for a grade 8 and neglected to mention that I needed an SAE grade 8 equivalent, as in frame bolt quality, only for the metric sized bolt I was requesting. I also didn't think to double check it. As a result, I am now the proud owner of a CUCV that has a starter with a mounting stud supporting a bracket that just hangs there, which is where I started. I also have a bear-nasty broken bolt piece that I was unable to get out of my block, and an extractor with a broken tip. I think I may have figured out a way to get a better line to drill the thing out, but it's going to be a bit of an undertaking.
For the moment, I'm trying to figure out a temporary support for the back end of that starter, since the general consensus seems to be that running without is a recipe for broken bolts and damaged flex plates.
Pulling my hair out,
Tinman