A Gen III Hemi is an option, unless you want to stay with the more traditional look of either small or bigblock. With heads that easily flow 340 cfm air and 426 cubes not hard to build, not to mention a stock valve train that will handle some serious rpm, I would think it wouldn't be too tough to do. Top off the stroker with a dual four barrel setup for the nostalgia look, and put a modern overdrive trans behind it and it should be a real blast that will go anywhere and not have to stop every hundred miles for another drink of gas. That is basically my goal with the 65 Dart I am building. A decent driver with some snap, although I need to keep it very streetable for the Mrs so nines are not in the cards. (no cage, wants AC)
If you want all out torque, then in my book go all the way. 605 with B1 heads. If you have to buy the all parts, you might as well. That should put you down in the low nines with pump swill. Maybe even high eights with some light parts on the car and an all aluminum motor. On the street, to go nines a small block will have to turn more rpm, just because of engine size limitations. That gives the edge to the big block in a lot of ways.