almost a necro post.
Still might have been worth it, The receivers sold for about a grand as of last I looked. The kits go for about a grand.
Hard telling what the problem was when the builder is deceased and the gun shop won't allow as test fire. Shit if you had a decent guy at the shop, I'd have conned him into a range trip and lunch.
First things I would have looked for (I say would have because this was 3, almost 4 months ago)
-gas cylinder; switched open and the port in the cylinder and the port and the barrel are lined up, very easy to install a gas cylinder on too far pushing past the port to port window.
-lubed right
-barrel on straight and not over or under timed.
-headspace correctly, short headspace and a usgi barrel and your up against it. reaming will only chip the bolt, and lapping the bolt too much goes through the case hardening.
Even if it didn't run I could make money on it.