I want to clarify that I MUST run 944 valves and not 951 valves? They are the same size, have no performance difference etc... Obviously the exhaust valves are sodium filled but this is for durability not performance and if anything they are heavier which is not great. Obviously you would not want to buy 951 valves because they are more expensive too.
The reason I ask is I have bought a rebuilt head that has new 951 valves in it already and I would hate to have to pull them out to put in my old ones or buy more valves.
Is this OK or is it a strict no no? Can I get a waiver?