5.9 magnum stock vs aftermarket heads for 400hp

Putting together a 5.9 for my 68 Dart. Curious on opinions about head choices/requirements to achieve 400hp. Fresh shortblock Lunati 711 HR cam airgap eddy intake 750 Demon carb Doug's 1 5/8's headers. Was going to buy a pr of Eddy Magnum heads but second guessing myself if there really required to meet my 400hp goal? I'm in Ontario Canada the Eddy heads end up close to 3k with tax. Or just build out the stock heads with some home porting ,improved springs for the cam and a quality valve job. Wondering if that could be spent in better places. Car is a Pro Touring build with great suspension /brakes etc . 518 trans and 3:55 gears
Thanks