Seems from what I've heard and read It's just in the initial break in period and first few hundred miles that cause the camshaft melt-downs. Once the parts are scuffed-in the problems diminish. A good assembly lube is a must on the lobes. My 86 Ford runs OK on regular oil but it's long been broken in. If your re-built sat for a long time before you ran it you may not have had proper oiling on start up, that's where damage can happen.
Could be the camshaft itself as well all camshafts are not equal.
Of course using zinc for the duration can't hurt.
Try Joe Gibbs break-in oil. Then Joe Gibbs Hot Rod oil or a similar product. It's about 9 bucks a quart but how often are you going to change the oil and how many times do you want to take out that engine?
