Fuel Mileage booster’s

For economy, on these old engine designs, your engine needs two things; 1) Cylinder pressure and 2) cruise timing.
as to #1; Cylinder pressure is the cure-all. Pressure makes heat which makes power, And Economy, by using less throttle to generate cruising power.
as to #2; Your cruise timing has to be up there, to get the small and widely separated components of the fuel-air charge to all react and contribute to making torque.

My little 2012Chevy Orlando pumps over 220psi at 930 ft elevation, and often gets over 40mpg from point to point on the hiway. For a 2.5liter engine it is pretty peppy in a 3600 pound CUV. The manual says 167 hp at 6700 rpm. Yes it has VVT, and is Direct Injected as well. It switches at 4500 and you can really feel it surge ahead. But I rarely go there as, the bottom end is sufficient.

The cruise timing tells the tale. To get the lean mixture all burned up inside the chamber requires a lot of advance. And your old Mopar will require even more. So much in fact, that your factory distributor cannot supply it all. Typically your Factory D can supply about 30 to 40 degrees of cruise-Timing, at 2200rpm. Which would be say 10* Initial, plus 10 in the mechanical plus 10 in the Vcan.
If you fudge it; say 16 Initial, 10 in the mechanical and another 16 in the Vcan= 42
But in all probability, after you lean her out a bit, she will be wanting 50 to 56 degrees.
How can you know what she wants?
The usual way I do it is to rev the engine in N/P to the known cruise rpm. I continuously adjust the throttle-opening to keep it there , while continuously advancing the timing...... until the rpm stops increasing with more advance. Then and then only, do I put the Timing-light on it. Whatever I get, I subtract 3* from that, and the result is the cruise-timing with a 3* safety margin to account for no load in N/P.
Try it and see what you get.
Now, how are you gonna give her what she wants?
If it gets to be over what the D can supply, and I guarantee it will, how will you give her the rest of what she wants?
What I have done on my car, is to purchase a stand-alone dash-mounted, adjustable timing-box that has a range of 15 degrees. My engine likes 60degrees in Neutral. So I give her up to 56* at cruising rpm, which is 2240rpm. That is 14* initial, plus 10* mechanical, plus 22* in the modified Vcan, plus 10 in the control knob = 56*
But my Mopar cranks 177 psi now , so is well able to pull 65mph=2240 rpm in overdrive with just a tiny amount of throttle. The previous cam made over 185 psi, and geared for 65= 1600/75=1850, she got 32mpgs, on one certain day-trip experiment.
Pressure and timing.
After that, there are lots of less effective tricks that all add up.