How much can be safely shaved without having to shave the intake or pushrods? Can I take .020 off.
In short, I came across a set of 58 Edsel heads with big valves, big ports and a bigger rust problem. TJR

It's hard to tell. Allways double check lifter pre load and and compare to. the factory specs. You need a dial indicator. Grinding off rust can be a lot on the clock. You don't want excessive lifter pre load.

I have adjustable pushrods and rockers, so pre load is not an issue. Manifold alignment and sealing is my concern. Any help or insight would be appreciated. I have shaved the heads .020. They are off to Slover's, absent a dire warning. TJR

Out of my stomach I think 0.020" is not critical to manifold to head and block alignment/ seal. But if the geometry was already a little off from the start it could become critical. Do a mock up w. feeler gauges in place of gaskets (compressed thickness as lsted in the gasket specs.)
You'll be able to see correct or incorrect geometry. A competent machinist will be able to grind off the correct amount from the manifold to compensate for misfits.
Good luck

I would think most any HI-PO machine shop will have a chart giving the info you need. I know FORD posted one (for the FE) in their HI-PO catalogs of years ago.