You're eating lobes because the cam isn't getting sufficient lubrication. The cam is not directly lubricated by the pump. Whatever drains back from the cylinder heads goes through holes in the lifter valley and drips down onto the cam lobes. If these holes were plugged, particullarly the ones around the #7 cylinder, the cam would not get enough oil. The cam is also lubricated by oil slung off of the crankshaft. If you had a windage tray or crank scraper, it may be affecting lubrication of the cam. A plugged pushrod would affect the amount of oil going to the cylinder head which would also affect the amount of oil draining back into the lifter valley and onto the cam. Oil galley plugs set too deep will block oil flow to the entire bank. Lifter bores that are too tight will keep the lifters from rotating properly, causing premature failure. Too stiff a valve spring will also do the same thing.

When you say you installed a new cam and lifter, that means you reused the other 15 lifters? That is a big no no.

Just so you know, I also recently built a 350 with stock Vortec heads, 1.52:1 roller tip rockers, and a Comp XE256H cam. It actually has more lift on the exhaust at .454", but has caused me no problems whatsoever.