I am puting parformance comp cams in my Mustang.

With no punctuation that huge sentence can be read at least three different ways, but I get the part about wear on a used cam. No professional would ever consider installing a used camshaft without at least keeping the lifters or cam followers matched to their lobes. The journals aren't the biggest concern because there should be no wear patterns on them, and they don't have the forces or speed acting on them that crankshaft bearings have. It's the lobes that wear to match the lifters. Lapping compound is for valve seats, never for the lobes. Most lifters spin in operation to prevent grooves from wearing into their bottoms, and that spinning is caused by a very slight taper to the lobe. Anything with grit, such as lapping compound, can remove that taper, and the grit can become embedded in the lobes. That grinding will cause more accelerated wear.