The 302 has the shortest stroke of all the small blocks. Chevy probably used it
only in a light car with a
really high perf top end for a good reason - the short stroke is best suited for an application that begs to be revved high like a Camaro with lots of sport/high perf options, aka the original Z28. Find a video of an original 302/Z28 running a drag pass, driven by someone with the cajones to run it right - it sounds like a chain saw compared to other SBC's. IIRC the 302's redline was something like 7,000 RPM.
More stroke = more torque. Torque is the ingredient most responsible for keeping a vehicle moving at fairly low RPM, which is what you need to have gas mileage and an OD trans. If your block really is an original Z28 302, it's going to be far more valuable to sell, in turn funding the purchase of a 327, 350, 383, LS swap, etc., than to keep in the truck and expect decent gas mileage and good "daily driver" performance out of when it's being used in somewhat the opposite role the engine was designed for: a heavy vehicle that's at its best with a smooth, torquey engine with a meaty mid-range under the hood.
Incidentally, your 3.73's was a common ratio for a lot of the late 60's 1/2 and 3/4 ton trucks, with no OD. The OD of a 4L80E, for instance, drops a 60 MPH engine speed of 2,600 (30" tires) down to 1,950. The OD transmission
plus 3.07's are going to drop the bottom out of that combo, to 1,600 RPM which is well below most gas engine's power curve. "Low-end torque" and "exciting top-end horsepower" were opposites until the perfection of variable valve timing and variable intake volume in recent years. The OD ratio in a 4L60E is yet faster than a 4L80, so you see where I'm going...
Just saying, I think you're asking an apple to be an orange by trying to build an economical, smooth cruiser around a 302 with an overdrive.
Incidentally, the Quadrajet is very much a variable CFM carburetor by the nature of how its secondaries work - so the "750" rating doesn't automatically equate to being thirsty. If you tune it right, and set the secondaries so they don't open when you just look at them, most of your driving will be done on the tiny primaries. My '85 1-ton, with a stock 454, TH400, 4.10 gears, and an 800 CFM Q-jet, would get 12.5 MPG in sustained 55-65 MPH highway driving because it was running on those two tiny barrels most of the time. But, when I'm coming around a 30 MPH on-ramp with a 9,000 lb. trailer and ask her for all she's got, put the hammer down, and hear a noise like a leaf blower start up under the hood, I know I've got all 800 CFM's on my side.
