Is overspray on cylinder head ok?

Too bad they couldn't spend a little extra time to mask off the valvetrain prior to painting. I personally would unbolt the rocker shafts and clean off the pushrods and try to get as much paint off the head surface as possible. Maybe use a lint free rag, with mineral spirits to wipe off the valve springs. At least you got the engine on a stand and can rotate it to keep solvent and debris from going down into the engine while you clean it up. Just my .02 worth.