Arouse the DAMPFHAMMER!
I totally agree with you @Lotus. I have investigated the ports and valves of the PRB, RBB, PPA and RSP head. None of them using flat retainers. There are differences in diameter, so that valve springs are not interchangeable. I have no clear statement to which one, just remember the PPA was smaller. Not sure if the RBB was it also to the high performance head retainers.These don’t look like k20a2 OEM retainers to me.