Welcome and nice car. I don't have anything to add to your new build plan really, but I just wanted to point out that you keep using words like "performance" and "fuel economy" in the same breath and the two just do not go hand in hand, sorry. Even tuned down, these V8's just are not designed for that purpose. My 302 has only been upgraded with the standard performance goodies and not rebuilt since it is a low mile car, but even with just the CAM, 4V carb, intake, headers and dual exhaust I probably average like 8 to 10 miles per gallon in the city. That's with the stock 2:79 gears still too and a manual 3spd. I plan on going to at least 3:25 on the gears this summer to make it feel more like it runs and since you have decided to do the smart thing and wait it out so you can do it once and do it right, I would suggest that you consider higher gears maybe since they won't be wasted when the engine gets upgraded, and for now, take a lesson from nature. Buy some cheap $40 glasspaks in place of the mufflers, and your car will sound so freakin loud that most will be afraid to race you. I never could understand why, but people often equate sound with power, lol. Like the tiny animals that have loud growls or stinky smells as a deterent to avoid a fight. Lol. Good luck!