6/71 due to its size . weight and it requires less bhp to run . if your bothered about heat introduce some water meth inj to bring the inlet charge down . the higher octane the better . think your spot on with your carbs for the street , if you can fit the blower cooler below even better . dont worry too much about the blower spining faster . wetten it up a tad more and it will be fine . torque wise there will be a difference for sure . 8/71 much better low end but 6/71 will be better mid range i feel and watch the 8/71 after 5000 rpm . thats why i would use the 671 as its safer and more suited to your engine size.