Looking for a little advice from you guys. I am getting parts ordered for a 451 stroker motor that will be going in my 69 Road Runner this winter. I used a Holley 770 Street Avenger on my 440 in the Charger and am happy with it, so would like the same on this motor. I am having a hard time deciding on the 770 or should I bump up to the 870? Edelbrock Performer RPM intake, Stealth heads, 10:1 compression, 4-speed, 28" tall rear tires, 3.91 rear gears (these might get swapped for 3.55), solid roller rocker cam (the grind hasn't been picked yet), TTI 1 7/8" headers with their 2.5" mandrel bent exhaust and h-pipe, Dyno Max Ultra Flow mufflers. The engine builder is estimating 520 hp and 560 ft. lbs. Spirited street driving. What say you engine gurus?