As
@losh1971 said need to determine how /why rusty .
I'm gonna guess car/engine has sat unused for a fair time with a gasket break /or no gasket, allowing the atmosphere/moisture in.
Do you know its history ?
Corrosion on outside of head as well .
Not to mention the condition of the manifold and injectors.
Again as losh has said SH ones =should be cheap as everyone replaces with roller rockers.
I'd also be changing the push rods = they don't look great either.
Check lengths of push rods =don't want to get wrong ones =your corrosion will be the least of your problems.
Also makes me wonder =OH what I can't see.