A few years back (about 5) I blew the motor in my father's '67 Continental Convertible. He had the 462 and the tranny rebuilt, and the car has sat with the motor out since that time. I thought the least I could do is put the thing back together for him, but the job has been more than I bargained for. After several set backs; clanky lifters, a leaky front crankshaft seal and an overheating problem, I thought I was almost done when we attacked a problem with the air conditioning. The air would work, but the diverter doors didn't direct the air properly. Armed with the factory service manual the restoration shop checked the vacuum. Low and behold the engine only makes 12lbs of vacuum when 18 is required to work all the accessories properly. Once again consulting the manual, we checked the the engine's compression, and every hole is low! All eight cylinders only make in between 105 and 110 lbs, the manual says I should be making 150. We tested the rings, and believe the problem is with the valves. Or... I remember reading on this forum that when a engine rebuilder not familiar with the MEL puts replacement pistons in an engine, often factory compression ratios are not maintained. The rebuilder is blaming sticking valves due to the length the motor sat uninstalled. I am wondering why EVERY hole would have low compression. Is it possible that all the valves are sticking?
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I guess it could be possible that all the valves are sticking, but I find it hard to believe that every cylinder would have the same compression. More likely they used a lower comp piston.
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Sitting for five years after a rebuild is not good (hopefully it was in a dry place). When one sits this long, it is best to disassemble and recheck assembly and prelube again. You say you had noisy lifters? Have you checked the oil pressure on the engine? It needs pressure to pump up the lifters and have compression (around oil rings). If the lifters are not pumped up, they may be causing the valve problems, if any.
You need to confirm oil pressure, and perform a dry and wet compression test to verify whether the compression loss is due to rings or valves. A leakdown test would be very helpful here.
And it seems that people are describing incorrect piston dome contour from suppliers.
After sitting for five years without startup, it is going to be difficult to have the machinist/rebuilder stand behind his work.
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