rocker arm geometry

I agree, the installed valve height has to be identical on these mopar heads due to the stationary rocker shaft configuration.

You only have a couple of options to change the valve geometry on these heads. You can either raise or lower the valve stem height (grind the valve stem to shorten, mill the valve seats deeper to raise), or you can raise or lower the rocker shaft (raise with shims, lower by milling the shaft cradles).

There's another option I've never personally used... you can install lash caps on top of the valve stems to raise the valve height. Some valve spring keepers will interfere with these and may need to be milled.

You can also switch rocker assemblies. They all seem to be different. I ended up trying several sets and finally found that Harland Sharps were right on for my setup (408 with 6777 Eddy's).

The rocker contact point should start inboard of the center of the valve stem, and as the valve opens the contact point (scrub angle) will will move outboard, crossing the center of the valve stem, and end up equidistant to the outboard side at max valve lift. To complicate matters, the rocker-to-valve stem angle should be 90 degrees at mid valve lift.

Google it and be prepared to become an expert. You may want to consider having an expert help if you're unfamiliar with it. Whatever you do, get it right before you finish the motor... dont' go half axx or you'll end up doing it all over again.