bout to tear into rebuilding a set of 500 efis , any recommendations? who to do headwork/refresh ?
Also what to look for / replace?
anyone with general experience?

Where are you located?? That is the main question.

How many hours, why are you rebuilding? Give us more info

the valve seats can get loose on the 500 heads check them really good, also the valve springs need to be changed at around 175 to 200 hours, also pressure test the cmi headers for internal leaks. 3 most likely items to kill a motor