No welder needed for the spraybar install, just basic hand tools. But for a .500 lift cam and less than 6K rpm, that wasn't the issue to cause such severe lashpad destruction, something else happened there. Did you replace the pads with new when you upgraded the cam the first time or just put the 40 yr old ones back in? Oil starvation is also a big issue in hard-pushed old motors. Even with a trap-doored, race prepped oil pan, I've watched the oil pressure gauge drop 20# around a long sweeper as all the oil gets thrown to one side of the pan and the pickup tube starts starving the oil pump. And we really need to clean out the oil galleys feeding the cylinder head when our motors are apart too. Are you using an upgraded oil pump or running an oil pressure gauge?