Re: Comp Cam lifters 5/16 push rod cups
This is a common issue with some lifters, in some cases, it's a SBF lifter and height is wrong too. I have seen some from Comp with sort of a chalice shape allowing either cup size, but your witness mark shows it's the wrong cup. I now only use Lunati Camsavers when building a hyd flat tappet FE for this reason. They have the correct height and pushrod size.
You can buy custom pushrods, which would not be a bad idea to address preload per cylinder too, but they will likely surprise you on cost for a 5/16-3/8. You can also buy a set of Lykins Motorsports hyd non-adjustable 1.76 roller rockers, he designed them with 5/16 ends to allow a much cheaper pushrod to be used. That is what I have been doing on hyd roller FEs because they have the same design
Likely easiest/cheapest way is to buy some Camsavers, they are also a very good lifter. Be sure to check preload though regardless, I have found that most FE pushrods are long from the factory, and valve tips are often all over the place.
70 Sportsroof, 427 FE/489 cid, TKO-600, 31 spline 4.10, A/C. modified Mass-flo EFI/reprogrammed A9L/CnC ported Victor.