With zero deck 7cc pistons.039 fel pros typical magnum heads are 65 cc you will be at 10.3 compression and a short duration cam you will probably be running premium. I did almost exactly that but a 318 and it was 9.9 and would just barely ping at low elevation hot days heavy loads. It took a lot of factors but I could get it to ping occasionally. All that to say I would not mill the heads. If you get EQs they tend to be about 1 or 2 CC smaller already so you will be pushing it.

I will have the 392 in my R/T running very soon, it is 10.2 with the stock R/T cam, long tube headers, air gap, CAI, orange 5.4 ferd infectors, lightly ported magnum heads and see how it runs on pump gas It is just in there temporary till I get the 410 ready to drop in.