Probably the easiest way is install an internally regulated GM alternator - like from a 70's Camaro. It'll probably take some creativity on the bracket from the old generator to the alternator.
And the starter will need to be replaced with a 12 volter too - shouldn't be a problem there.
Then replace all the bulbs to 12 volt bulbs.
Ammeter will still work fine, gas gauge may show 1/2 when full.
And of course, a 12 volt battery.
Don't toss out the 24 volt generator, regulator or starter - there are purist buffs that will want them.
One thing you have to deal with is the cloth covered wires - not good insulation, especially after 50 years.
Sounds like a great find.
And the starter will need to be replaced with a 12 volter too - shouldn't be a problem there.
Then replace all the bulbs to 12 volt bulbs.
Ammeter will still work fine, gas gauge may show 1/2 when full.
And of course, a 12 volt battery.
Don't toss out the 24 volt generator, regulator or starter - there are purist buffs that will want them.
One thing you have to deal with is the cloth covered wires - not good insulation, especially after 50 years.
Sounds like a great find.