Rotating exhaust valves

Yep, multi groove locks touch each other when they are assembled so they don’t totally lock on the valve stem. It makes them rotate.

I know guys use that style lock with solid lifters but every time I’ve seen it done it beats the hell out of the valves and locks in pretty short order.

Hydraulic lifters don’t mind because you don’t have the lash beating on the lock.
I've never seen slant sixes do that and they all came with four groove locks on the exhaust with solid lifter cams up to 1982.