Holley Carb Jetting Help, Lousy Fuel Mileage

Wow, the lowly Pro-jection is showing some love, eh?
I certainly don't love mine. It requires regular tweaking of the knobs, even with O2 feedback, and seems worse since I switched to the little "2D" box. I do have ideas to improve Holley's design.

That wideband up the tailpipe needs to be WAY up the tailpipe as any O2 that is sensed should be coming from the cylinders instead of atmosphere. ONly way I can see it working properly is if its as close to the collector as possible, nice and hot.
Many after-market places sell a tail-pipe mounting kit for permanent installation. It only needs to be far enough up to insure it isn't seeing air from outside. A wideband sensor has its own internal heater that always runs (not just warmup like 3 or 4 wire regular O2 sensors). Indeed, you can ruin the sensor if you run it long disconnected. Without the heater running, the passages can clog permanently with soot.