would it be hard to replace gen with 12 v alt and convert tractor to key swith 12 volt start, and would i need to change out starter or could i use 6 volt starter, Thanks Jim

I changed my WD over to a one wire GM alternator and 12v system over 25 years ago. (had a wiring fire, seemed like a good time)
The 6v starter has not needed service since the conversion and man does it crank! I think they actually last longer at 12v.
I converted the contactor stud to a threaded stud, which if I remember, was a stinker to solder.
I used a pre-computer type Ford soloinoid, mounted on the gas tank bracket. Not oem, but very funtional and trouble free. This solinoid also has a terminal for the ignition that can bypass your ignition resistor, for full voltage to the coil when starting. (just like a car)
I use marine type battery post terminals on all my batterys (with the threaded stud and wing nut to attatch the cables) Makes it quicker and easier to swap or disconnect the battery. Again, not oem, but handy.
I disconnect the ground cable when parked in a building, fire parranoia.

Switching to 12 volts easy switching to a key type start no as easy because of the way the starter button is. But if can be done because I have a C that is set up that way just takes haveing things change on the starter which would cost a few buck. 6 volt starter will be ok but you need the switch stud replace to a cable type stud

• Hobby farm

Search the site several times the procedure for adding an alternator has been discussed with the wiring diagrams. The starter will handle 12 volts the way it is, but with the design of the starter I don't know how practical a key start is without a major rebuild to add a post or solenoid.

No it is real easy. You can still use the 6 volt starter.
Send me an email and I'll give you some info.