Reply to "New Carb recommendation"

Re 750 vac-sec Holleys: the old rule of thumb was, a #3350 (750) just bolted on in place of a vac-sec 600 would gain you about 20 bhp and lose you about 3 mpg while softening the throttle response. Re-jetting would gain back some but not all the mileage lost and a little of the response you lost going bigger. In an autocross, you'd set a better time with the 600.

Re having a carb-tuner work on a bigger carb prior to trying it: the tuner I use in N Reno makes 19 separate changes to the carb out-of-the-box, not just jet changes. That's why the cost of the carb doubles.