Help with Flathead Ford F-4 Truck

If I had one, I'd probably "go 12V" "Probably" the minimums:

All 12 V bulbs, of course

6V starter works fine on 12V

New starter solenoid, they are cheap. I might be tempted to gamble on how long the 6V one lasts LOL

Electric gauges, use a "Runtz" regulator for each gauge, or if you are handy, you might get by with the 5V DIY regulator projects aimed at the 12V Mopar Ford instrument limiter repairs

Heater, wipers. Use parts store "volt drops" and follow the destructions. It depends on amperage draw of the particular motor

Coil / ignition. Get a modern 12V coil and matching ballast. Doesn't matter what they are off of so long as they match, IE "68 Plymouth coil and ballast"

Generator / alternator. You can use ANY 12V generator so long as you have the MATCHING regulator. Almost any alternator you can mount will work. Cheapest easiest regulator is the 62--69 Mopar 2 wire regulator Most of the time, this regulator will work fine on all but the heaviest alternators