I did up a mild set of E heads for a 408 last summer.
Pump gas(I think it was 10.7cr), 265-270cfm heads, victor 340 intake(customer already had it), small solid roller, .600/.600 with 1.5 rockers,(customer didnt want a flat tappet cam, but did want 7000rpm capability)....... Made 540hp...... Don't remember the TQ exactly..... I seem to think it was 520-530tq.
Don't know what the bill was, but I'm pretty sure it was over 6k(parts, machining, head work, assy, dyno).

500+hp from a pump gas 416 with eddy heads and a hyd roller isn't hard at all.........having it "all" done so all you have to do is write a check, and have it end up at under 6k.......that might be harder.