So I'm getting ready to rebuild a 340

If it will be a daily driver, then a broader torque curve and better bottom end performance will be the right approach; you will spend most of your time in the 2000-3500 RPM range. You can do this with a 340 (or any small block) without going stroker BTW. The AL heads will get you top end breathing so you can wind it out when you like, and then the cam and piston/compression ratio selection will set the low RPM range in general. A moderately high Static CR in the 9-10 range will do the trick to help low end torque on the street at lower RPM's.

The Edlebrock Performer 63 cc heads (PN 60779 with valves and springs) are hard to go wrong with for the AL ones; the breathing is good for a bit over 400 HP right out of the box. Any HP in the 325 range or above is likely going to set you back in the seat with a happy smile on your face if you are new to the V8 world. You'll need to pick up some rockers to go on them.

And, if you don't have the block or engine yet, a 360 may be a better base to start from simply because you will have a wider piston selection to work with. It, in essence, is a mildly stroked 340.

Will you be looking for good fuel mileage? And of course, there is the question of your budget......