I'm going through the same thing. Funny, but it is #5 exhaust on my 351C that went flat. I also heard of a 427 with the same #5 exhaust flat. I broke mine in without the inner valve springs and did everything by the book, but the Reed cam went flat and ate two lifters in the first few miles. The lifters were turning too, as the wear pattern was even. I just flushed the engine, then replaced the bearings and
oil pump even though everything looked just fine. Also epoxied 4 magnets inside of the
oil pan for good measure.
BTW, once I built an engine and used lots of Comp Cam Lube and after setting before startup for over 3 years, I had no cam problems. Pretty good stuff. Pre lube with a drill before starting.
The machine shop I use sometime always uses ARP Moly Thread Lube on cam lobes and lifters. He swears by it.