If your looking to make peak power around 6200-6400 rpm with a 340 my guess that's about 450 hp. If your trying to build with good mileage and driveablity I do it like how LS and modern hemi's do it lots of head air flow and mild roller cam. Normally most would use 240-260 cfm head with 10.5:1 and a 285 ish cam to reach your power goal, I'd go with at least 280-300+ cfm heads with high rocker ratios to put you in the heads air flow sweet spot and keep the duration relatively small, once you decided on heads I'd play with different cam timings in a dyno program.
