The fact that the oil pressure is up there very good news. This eliminates the bottom end as the source of the knock. When you rev the engine, is it blowing any smoke from the exhaust? What colour is the smoke? Does the knock tend to even out at higher revs?
Short of carrying out a compression test on each cylinder, I'd remove the muffler and air intake hose at the manifold, and crank the engine with the stopper out. If you hear any sign of air leakage, (slurping) to a certain degree when turning the engine over, I'd suspect either a badly seating exhaust or inlet valve, or more likely a blown head gasket. The latter is most likely. As I said, a compression test will soon confirm this. Let us know your progress, Evan.