I get 8mpg with my 408. it's 8.65:1, however, fulltime OLSD, with no mpg cruise tuning, running 96lb @43.5psi (so 116 at our fp) injectors. You won't need anywhere near that big of an injector for NA (although you likely need 60s for 600rwhp). I have stg III TEA full race heads with 2.08 / 1.60 valves. Cam is pretty mild for the cubes == 236/230 on a 115 lsa

Note that's all city and is a historic average (day to day is probably much higher, but this accounts for mashing the go pedal, which you WILL be doing a lot of

 

Mpg is why I just went 370. Now I almost wish I would have done a 347 but I'm FI...different animal.