my used cam

Let's not just seem like we're bashing, lets give the real reason. Here it is. Camshaft lobes are ground on a taper. In other words, they are not flat across the lobe. This is done to make the lifter spin it its bore. The lifter is also not flat on the bottom. Is it ground with a convex (dome) shape across the bottom. This also facilitates lifter spin. This means that the contact pattern between the lifter and the cam lobe is thin. This is why camshaft break in is so critical to a flat tappet camshaft and lifters. This is done so that the lobe and lifter will not fail when properly broken in. If the lifter did not spin in the bore, the camshaft lobe would wipe in the same place on the lifter face and soon destroy it.

For years, it has been accepted that you can run a used camshaft with used lifters, as long as those lifters were kept in order from each lobe they were run on on the same camshaft. It is also accepted practice that you can run new lifters on a good used camshaft, providing you run through the break in process just like a new camshaft and set of lifters. In this way, the new lifters wear to the used camshaft's lobes. Again, this is acceptable.

However, under no circumstances should you ever run lifters that have been run on a camshaft if they have been mixed up and you do not know which lobes they are asigned to. Not even on a camshaft that has five minutes run time, much less one that is already broken in as you describe.

You've broken a cardinal rule and WILL have a failure of either a camshaft lobe(s) or lifter(s) or both. It is simply a question of time. Why a "professional" from a suposedly "reputable" camshaft company would tell you it was fine is beyond me in light years. Rest assured, it is NOT fine.

If this engine is together and running, I strongly advise you tear it back down and closely inspect the camshaft and lifters. Drain the oil and look for metal particals. If you see none, oh happy day. Buy a new camshaft and lifter set and replace what you have. They are now worthless. Just hope that is ALL that needs replacing, because if you have metal particals in the oil, the entire engine needs to come down.