Amount to mill heads

Ok I have a LA 273 1968 engine 2 brl I'm rebuilding std bore , std pistons , std rods etc i had crank polished ( std size also ) rods and pistons cleaned ok cam is 484 / 484 lift have adj rockers want to have heads milled to increase compression to 10.1 how much does it need to have taken off ? Will I need to mill manifold side too ? Need advise thanks