I for one think a 6.4 long block with a tall drag pack intake and quality headers would be a killer "buy it and drop it in" package, MSD ignition and a carb is about as cheap as it could get and it's cheaper than building a 392 stroker 5.7. The SRT 392 is 485 HP in emmisions NVH and MPG choked form, you add a much better intake, tune and exhaust and give it a gross instead of net HP rating and I bet you can find 575 HP at the crank. I know its not 700 hp but it would be a whole barrell of fun for minimal investment. A cam upgrade should be able to put you solidly in the 600 HP range.