I build and dyno a bunch of FE strokers - probably more than anybody in the US. Depending on your goals, we see engines in the 500 range pretty often with the 445 inch versions - 4.250 stroke.

While a 500HP 390 is a rumpity rump racy deal, a 500 HP 445 stroker is tame as a kitten in comparison. A 294S Comp solid flat tappet gets you 494HP at under 6000RPM. A milder 282S cam is very driveable and gets 475 HP and a mild choppy idle.

Feel free to drop me a PM or email and I can walk you through the various combinations.