Update for those with any interest in getting MPG out of a 40:
Since jetting, and finally fixing what was a much bigger fuel leak than I thought, fuel economy has been as follows:
I just capped the vacuum retard distributor, and I feel that will give me a bit of a boost. Other things that will help me reach higher numbers are as follows:
-fix the grindy input shaft bearing in my transmission OR
-install a decent 4-speed transmission
-remove the air pump setup (reduced losses)
-intake (not sure if there's anything out there for this)/exhaust header
-33" tires might help a bit, but they might hurt as well.
My initial goal was 15 mpg, and I did it. If I had more of a budget than I do right now, I think 18 could be achieved with a more or less stock F-series engine.