Spring/Keeper interference with Rocker

I am not certain at all that the springs/retainers are responsible for all the cutting on the rockers. Based on the deposits on the cuts in some areas, parts of the cuts have been there for a long time. OP, are there any wear marks on the edges of the springs or retainers? I cannot see any spring/retainer wear in the pix, but I may not have the right angle.

I'd start with checking the springs' outer diameter; SBM is 1.460". BTW, the retainers being smaller than the spring is common but this looks to be a bit much of a size difference.

Then check spring installed height from top of spring to the head; SBM is 1.650". If these are long, then rockers will be tilted up and more prone to hit the retainer/spring edge when closing.

Being that this appears when hot and the oil is thinner, it could well be a lifter. A short/bent pushrod is also possible as well as an exhaust leak at one port.