.0123 is stated by Direct Conection books.

.042 of head will reduce 1cc volume as far keeping on open chamber section.

Yeah pistons is better but 400 doesn't have too much options off the shelf. So mill is a handly solution to help. 440s have lot of options though

Even better, aftermarket heads too

depending on what you want to get of course will be entering on troubles or not

With a Charger born in Chrysler assembly plant in Valencia, Venezuela