if you have a leak down tester you could check a cylinder to see if there are leaks at the valves, rings or head gaskets?
ON a new rebuild I had low compression, the leak down showed both valves were leaking and both heads had just been rebuilt. I called the machine shop, a friend of mine is the owner. He had done my heads and I trust his work. He laughed at me. Said run it, the valves will seat perfectly and don't worry about this pre run test. He was 100% correct. Never had an issue with that engine. I had forgotten this until you asked questions. This shop uses a nice Serdi Head Machine so quality is always very good. MIght be the same for your engine???