I think i broke rear main bearing

Well then, we will see how I do. I’ve got a BBC on the dyno that has a helicoil in a head stud hole.

I’m betting it won’t fail.

The chances of fitting a main cap and cleaning it up with a line hone is slim. You have to line bore them.
It might not fail with a stud, I've seen them fail with the use of bolts. I do wish you the best of luck.