advance springs

The timing requirements for a lightly loaded as compared to heavily loaded d100 will be different. I would talk to dusteridiot on .org for advice.

If you really want to micro tune the ignition, I would suggest investigating a EDIS/MegaJolt setup. The same thing can be done with a Micosquirt and LSX coils. This would give you a fully programmable crank triggered ignition.

not looking to get that crazy. 90% of the time I'd say "lightly loaded". maybe 95%.
want to stay mechanical, carb'd. yeah, I know you can get crazy adding electronics into the mess, but not interested. Electrical/electronics isn't my cup of tea.
Working on much newer vehicles at work, I get hung up too often as is, when all this electronic wizardry goes nuts. This truck is all about K.I.S.S. (keep it simple, stupid) trying to stay as far away as possible from "check engine" lights, a ton of sensors, codes, and such. All while making it "the best it can be for what it is". add in the "hey, look what I did" thing.

there is a certain umm, I dunno what to call it, satisfying feeling in mechanical controlled repeatability without bad grounds, smoked sensors, corroded wires, don't need a scanner or other computer type device to figure out what's wrong with a truck. and mechanical settings can be changed easier (for me anyways) than electronic ones.
Plus I'd rather be closer to being able to fix any problem that might show up "with a screwdriver" than a scanner, laptop, a pile of schematics, etc.