For longevity, you are better off with a 331 over a 347, most 347's end up with the wrist pin behind the oil rings because the piston are so short, another draw back is also because of the short piston they tend to rock in the bores when the engine is cold and flog them out. There are plenty of ways to reach your power goals but you could help us out by telling us what your intentions are for the car (also what car it's going into), is it a street/strip car, with emphasis on street (and if more street than anything will it be a highway cruiser or an around town brawler) or strip (those can be two pretty different combos) or are corners more your thing, or even just a cruiser that sounds good and is capable of the occasional skid, what is the running gear you are planning to put behind it is it going to be a manual, is it going to be an auto, if it's going to be an auto which one and how much high stall are you willing to run, what's your rear end setup and do you have and what ratios would you like to run the more info you provide the better people can help you