what valve seals after machining guides?

I wanted to check back here and make sure I wasn't totally out in left field with the lifter angle thing you were asking about. Turns out its a well known quirk. Sorry for any wrong/incorrect info or suggestions.

The only thing that really has to do with pushrods here is that they are what connects the lifter to the rocker. Using a checking pushrod holds some merit in a general sense but really has nothing to do with what you are asking here and could not possibly solve the issue.

I didn't find anything specific about how much lift is lost due to the angle but I think the general consensus is like MRL said, not much. Maybe a few percentage points or like you stated earlier, a few thousandths.

Back in the 70s Dick Landy and Bob Glidden were plugging/sleeving the lifter bores on small blocks to get better angles.