It's been a while since I last tackled this brake problem I have but I figured I'd give an update, it helps me remember also.
Trying to fix the right rear lower caliper guide pin hole, I ordered the dorman pin that is oversized and designed to cut new threads. That didn't work well. It went in and started spinning. As I took a look I noticed that the threaded hole in the caliper bracket is now an oval shape, it seems the top one is almost the same. I'm not sure if rust caused this or a previous owner did.
As far as thread sizes go, im still a bit confused. The new oversized dorman package says it is 7/16-20. I can not thread a 7/16-20 die on that pin at all.
Using a die on the normal ac delco pin ,18k92, I can nicely fit a 1/2-13. This does not make sense to me. So I believe the pin is a metric thread.
My next course of action is to remove the axle then the caliper bracket and take it to a welder to weld plug the holes and start over. Hopefully he lines them up right. The caliper brackets used are very, very expensive.