It is the keepers, not the retainers, that interfere with the self aligning rocker arm rails or nubs when using valves with .250" tips.
I furnished my engine builder with the Ferrea 5000 Series SBC valves with .256" tips and later found the problem with the keeper to rocker rail interference. After discussing the problem with my machinist, he told me the Chevrolet heads that use self aligning rocker arms have valves with .260" tips (int.) and .289" tips (exh.). He recommended Manley Race Master Series SBC valves with .290" tips, intake and exhaust. Manley Race Master Series 11863-1 and 11860-1 valves with .290" tips provides .035" clearance between the10* keepers and the self aligning rocker arm rails, when using beehive valve springs. I am using 10* keepers which are wider across the tip of the valve than 7* keepers. When trial fitting the Scorpion self aligning roller rocker arms with the Ferrea SBC valves that have .256" tips, the self aligning rocker rails actually rode on the the 10* keeper and not on the valve!
The beehive retainers are smaller in diameter (1.055" O.D.) and sit lower on the valve stem than standard valve spring retainers and do not present a problem with self aligning rocker arms.