F cub need advise

If it were me, I'd go to the GM 3-wire internally-regulated alternator...and find a rebuilt starter. And I'd replace the radiator, simply due to the fact that your tractor is a minimum of 25+ years old, maybe as much as 60 years old. But also check the casting below the radiator for cracks, usually about where the bottom of the grills sits. This is a common point where tractors that have been frozen up break.

While these things won't be exactly cheap, in the long run you'll be glad you did them. No sense in having 'half-fast' repairs come back and bite you.

Getting a used or rebuilt generator (versus convertign to alternator) could save time and wiring modifications plus keep her ORIGINAL..... ... But then you gotta hope the Voltage Regulator or Cutout Relay is also okay cuz a rebuilt Genny PLUS a new VR/Relay may get pricey as compared to an alternator. NOTE the GM 10 SI 3 wire is readily available and cheap as compared to a One Wire although the one wire is easier to wire up.

One of the most expensive components of a starter is the armature, Id shop around for a good used unit and compare it with what a rebuild shop will charge to fix yours.....

Often an old rotten radiator may be patched but will spring a new leak later. Same as above Id shop salvage dealers and compare it to the price of a refurbished unit.

Its just hard to say sittin here and unaware of your budget and the availability of salvage dealers and rebuild shops in your area. Still if you spend a few more bucks now n do it right (rebuild versus salvage) you may save time n money n aggravation in the long run, that would be my approach.

John T