Big Block Rocker Shaft Shims

I think Dan Dvorak sells what you're talkin about. But first, not ALL Mopar engines have incorrect valve train geometry. That's the stupidest thing I ever heard. Yeah, I am sure a lot of them ain't perfect, but for the most part, they are Purdy dang close. Close enough to run for 100K or more miles. I think the shims you're talkin about actually relocate the rocker shafts either toward or away from the valves to get the pad or roller in the right spot on the valve tip. There was a guy on Ebay that sold them to whatever thickness you needed, but I don't see him on there now. Maybe Dvorak can help you out.