496
049/781 oval port cast heads are the best stock heads. However, even mnoidified, they will hold back a 496 engine above 5500 RPM.
To do them right you need to add 2.250"/1.880" valves, unshroud the bowls, port match, have bronze guide liners installed, mill the decks, add good rocker studs and guide plates. Then figure in good valve springs, titanium retainers and 10 degree locks. But they will still be less than 290 CC intake ports. Too small.
A set of RHS/Pro Topline 320 aluminum bare heads can be bought on RJ if you look for $1000. They will take the same parts but the machine work will be done already. They will make 75-100 more HP. And they will have resale value.
If you have to use stock heads, sell your 2 sets and buy a set someone else already spent their hard earned money on doing all of the above, for about $500.