If you have to spend more than $600 on a refresh, then you must go Aluminium.
But I would never spend time and effort on a 516 anyways!
I have wrecked several pairs trying to get the exhaust ports 'into shape'.
Some are cast with the very bad roof port bulge that cannot be enlarged.
But I recently came across some 516 castings 1964 and 1965 that have the later style '915' 'LARGE' exhaust port, go figure?
All the 1966 heads that I have ported and subsequently ruined have the collapsed roof...
So I cut my old 1966-516 race heads up to see why?
I'm guessing its a 'foundry flaw' with damaged casting-moulds from 'over use'...
Pictures to follow for anyone who 'maybe' interested lol...