We had as much as '50' milled from head surface and then '60 from the intake side and immediately noticed the much thinner valve cover gasket contact surface on those intake sides. Not a problem but something to be aware of. We went with the more durable (but thinner) black V.C. gaskets - as opposed to common cork/rubber.
First of all you cannot swap heads from a 440-3 RV/industrial motor. The 440-3 has extra water cooling in the block and heads and if you use a RB heads from a passenger car or truck yaou will have nothing but cooling problems. I was involved in 1984 with Chrysler and overheat on motorhomes and we used Pikes Peak roadway for our cooling testing.
you just need the bore and stroke, piston type...i.e. flat top dished or domed CC, depth of piston in block, CC of the head, and gasket thickness. Its really cool because with this you can vary say the thickness of the head gasket and see how much that raised compression. Or the CC of the head. In my case i have a bored and stroked 360 so 4.030 bore and 4.00 stroke, with 64 cc heads (decked j heads...machinist cc'd it for me), and the pistons are dished 20 cc, with a .050 head gasket that came with the gasket kit. Works out to 408.18 Cubic inches, and 9.77 compression. Interesting to note that if i went with thinner head gasket .040 available on summit compression rises to 9.97 or if i went with thicker .056 gasket it drops to 9.65. Now...getting COMPRESSED gasket thickness is not an easy thing for some of them.