what e clip for a hyd lifter retainer

I shim the plunger while clip is out.
I usually leave about 15 thou for drag racing.
NHRA in teardown in Stock until a few years ago
used to check to make sure some oil bubbled out
of the lifter back when Hydraulic lifters were required.
I still run the same camshaft today(200 on seat) with Schubeck Ceramic
lifters. It sees 7700 some times when needed.
My boy in same class runs Billet cams ($1000) and tool
steel coated solids ($900) and 300 Lbs on the seat. He has
catastrophic failures every 30 or 40 runs.
They both run about the same mid 10s ET @3300+