looking for new heads for the gt40

I think you answered this question yourself, you have 2 dead holes, one on each bank.  Your heads need to come off for repairs.  Your oil test tells you the problem is in the valves but one more thing to check is the camshaft, make sure the 4 and 5 cylinders valves are opening and closing properly.  If the 4 does not open valves as far as your #3 that would point to a flat camshaft lobe but you need to measure lift not just eyeball the lift.    Most likely you need heads.