....I've got it.
Three drives with the Miles to Empty computer working revealed that for every 1 mile of odometer increase it was drinking roughly 4+ miles worth of fuel.
My friend Chris decided to price out the parts for an ignition refresh, and at just over the cost of a tank of gas, and after examining a plug and the distributor I decided it was worth a try. I bought a new set of copper plugs (I considered Iridium, but those plugs alone would have cost about what everything cost using copper). We changed out the Plugs, wires, cap, and rotor (there are no points in my ignition system thanks to the Duraspark system). The last two on the list were substantially worn.
After the work the Miles to Empty computer was ticking off the miles in step with the odometer so unless that computer suddenly changed calibration it is safe to assume my mileage quadrupled. I have not yet calculated it (need to run it down 1/4 while clocking the miles), but assuming my last calculation (which IIRC was during a different state of carb tune than prior to the ignition work) was close to it's last poor-ignition value I've probably jumped from ~6MPG to ~24MPG....I tested it on stretch that was (prior to the work) consuming about 1/4 tank, after working on it that same stretch is barely moving the needle.
Best money I've spent on repairs/upgrades yet!
