The part according to Chevy Master Part Books is listed as GM# 3835392 - Cap - rotator assy. valve spring.
Used on all 1947-62 6 cylinders for both intake and exhaust, except for Commercial 1-1/2 ton and up truck 6 cylinders that used different "rotator assemblies" on the exhaust valve of the heavy duty 6 cylinders. They do not interchange with the V8 or later 6 cylinders.
Very limited availability from a quick web search tonight. I found
12 NOS pieces available on evilbay, but the seller wants $19 each for them - OUCH!
I did find that EGGE Machine Company looks to offer a
Valve retainer 3835392 listed at $5.89 each, but unknown if in stock or not.
Hope this answers your questions.
