Bolt size?

I'd take mine down to a good hardware store and simply match them up with a good Grade 8 and go from there. I don't know what size they are, but they are not hard to find. If you have reservations with using bolts from a hardware store, then go to an autoparts store that has a collection of bolts. I use my local NAPA Store, they have lots of automotive bolts.

For my `79 CJ the hangers are held to the frame with two 1/2" x 13 bolts.