Six Pack question

My opinion only:
You have to want a Sixpack for eyewash only, and be willing to spend for it on that basis only. It will probably make a little more power than your 750, and it might, MIGHT, get better gas mileage, as stated above, only if you keep your foot out of it.
But it would have to give you thirty mpg for ten thousand miles a year to pay for itself, and that ain't gonna happen!
For reference, I love my Sixpack big block, and I have another new manifold, but the cost of carbs vs performance increase over my 850dp is negligible, and I won't spend for Sixpack carbs for eyewash.