Heads depending on condition 650-1000 is not uncommon

however if you are after performance the japanese
use the old round port heads weld up the chamber
as they are smaller and easier to achieve a modern
race chamber also they fill up the ports and re-port
them higher up for a straighter flow all topped off
with 40mm in/ 33mm ex valves which are not the
biggest but do what they have to do.