410 LA small block will not rev past 6000

Don’t shim the valve springs. Your set up. Rocker to pushrod angle and valve tip placement and travel are next.

I was thinking lifters next if it’s a hydraulic.

Then the actual port flow of the head because i mimic what is said above. Very possible the head is undersized.

I think the intake is fine for the application. Ported or a single plane should deliver a few more rpm. The dyno graph crash is weird.