Spring/Keeper interference with Rocker

might be a perfect storm of mismatched parts, poor assembly. With an aftermarket cam, there can be geometry problems. How much lifter preload do you have?
I noticed in one of the pics the valve stem tips looked a little galled, maybe from poor oiling or maybe just poor machining when heads were done.
Sometimes the addition of hard seats can make the tips uneven. Sometimes sinking the valve seat by "falling asleep on the seat grinder" can sink a valve seat and thus make them uneven.
Keep investigating, you'll figure it out. On the plus side, the engine looks quite clean inside. In the meantime, I think I'd invest in a couple of FilterMag oil filter magnets, just in case there is some metal clearancing going on.