Daily driver setup

Use the stock electronic ignition that you have.
HEI upgrade makes the ignition reliable.
The od and high rear will actually hurt your milage because of the drop in rpm's between shifts.
I would put a straight 4-speed in it or at least change the gears to 3.23-3.55 if you use the od.
Use the holley 1 bbl, super simple carbs that work and you will see 20+ mpg.
Just use what you have and keep tinkering, I have not seen a slant yet that got really bad gas mileage unless it was really out of tune.