Broad question from a rookie
Keep the 904 and build it with good components. Plenty strong enough especially if you aren't drag racing it. Lighter than a 727, uses less hp too.
Ported iron, LA-X, Ede, procomps there are a bunch of heads... flow is where it's at for making HP. Stock ede's won't make more than a true 430-440 without porting, just not enough port volume and air flow, regardess of what many will say.
I'd find a Hyd Roller block and build that as the roller stuff works well and cams are easy to get.
Camshaft depends on how rowdy you can handle at idle. :)
You don't need a stroker to make 400-450.
Brian at Indio Motor Machine is pretty good and has a nice handle on building stuff.