I made the right decision: machine shop
I took the used motor to the machine shop to have them extract the broken front mounting studs, because I didn't feel like doing it myself. They called today, told me it was done, that it was $42.
$42?? I thought. Seems like a lot for a couple of easy-outs, but whatever. It's done. I went to pick it up.
Turns out one of the studs was also broken inside the hole. Not only did he have to get the remainder of the stud out, but he also had to helicoil the hole.
Considering that I don't have easy-outs or a helicoil kit, I think that $42 was well spent. I've also got a bike lined up to put this on, for free, from my mother-in-law. I just hope the frame is suitable.