Shouldn't he do a leak down test before disassembly just in case it's the rings (or ring seating). If he plans to pull the heads (even though he doesn't have to) to replace the seals which is the only way he can check the valve guides??
Absolutely, that is a good place to start. at a minimum a compression test. What do the plugs look like? oil fouled or? The different valve stem height would have stopped me from installing them.
