Other than what's been said here, the only thing I do differently to distinguish from an engine in decent shape versus trash heap is I pull the head off and turn the engine over swiftly. I stick my nose over the cylinder and note the 'pop' and air (fuel charge) flow from the transfer ports. If you get a good pop and can feel a little wisp of air coming from the transfers, then it should run at the very least 'O.K'. If it doesn't pop good and the air flow is minimal, it's at the very least in need of a new ring(s) and light honing.