318 problems

I bought the car 2 and a half years ago and I was told the engine was rebuilt 3 years prior. Of course, two months after I bought it, I had a head gasket blow. I put 5000 miles on it, so at best guess I'd say 30,000... but really I have no idea. I'm going to go get a loaner compression tester from Autozone, but I've never done one of these, so is there something particular I need to look for?