Bob,
I can't say that I am expert in all the varieties of valve springs and valve collars, but I wonder if the wrong combination, perhaps from an iron head, would reduce the overall valve travel that is available.
My inclination is to think the scuffing is due to something else, not having heard of valves lacking adequate vertical movement (unless, of course, they are hitting the tops of pistons due to a mess up in timing gears, but you would have heard that rather loudly, and probabaly not have been running).
Running out of valve-spring travel would, I think, lead to bent pushrods. How are those looking?
How are the tappets? Are they nice and free to move in their cubbies in the bottom of the barrels? Are their surfaces scuffed and/or deformed?
Another possibility is that the cam was reground without rehardening the surface.
Perhaps the last engine rebuilder forgot to use assembly lube on the camshaft and tappets when the engine was rebuilt and, then it was just too long before the cam lubricating gallery got filled after the engine was first started.
OK, that just about exhausts my ideas and, unfortunately, I can't say with certainty that any one of them is a slam-dunk. I trust some others here will correct me, confirm me, or add to the list.
You might want to post a photo of the cam to give me and others a better idea of the type of damage.
Richard L.