Build the 511 or 512 C.I., shoot for 10.0 to 10.5 to 1 comp. ratio for 91 pump swill and look at buying a cam that is bewteen 250 to 265 degrees at .050 cam lift and have it ground on 106 to 110 lobe centers, depending on where you want peak torque and HP to be 106 will build more bottom end and run out fo breath sooner, 110 LSA cam will not have as much bottom end, it will idle nicer,not real racy sounding, but it will pull harder from 3000 to probally close to 6500 RPM. Lots of chaoies out there, good luck and have fun The 512 with a bigger cam will make 575 HP and over 600 ft lbs easy on 91 octane pump swill, it might even be a challenge to keep control of the rear tires in a standing start with aggressive use of the throttle