Welcome.

Your electrical question is far beyond my capability, but someone will come by with some answers or suggestions. Having said that, I would probably be searching for the original generator and a wiring diagram.

 

I think your two 12 volt alternator idea is a fire looking for a place to happen. On 24 volt system the starter,generator & regulator are isolated from the tractor frame. 24 volt systems have a long history of shorting out and catching fire. Save yourself some headaches and convert the tractor over to 12 volts. It can be easily converted for about $500 utilizing a new 12 V starter and Delco alternator.

 

In theory, the twin alternator setup could work, but by the time you find the alternators, fabricate mounts, wire it and install circuit breakers to prevent fire, you would have far more invested than buying an original 24 volt generator and regulator, or convert it to 12 volts.

 

You could use battery isolators and charge each battery off the 12V alternator and have 24 just for starting and lights. Same principle on some electric golf carts.

 

Since you have a 24 volt alternator that's not charging, I would fist have it checked. It may not be the problem, but a wiring issue instead.

A friend bought a 24 volt alternator to charge the "house" batteries of his bus. He could not get it to charge. We figured out it was not wired to "see" the house batteries voltage, so it would not charge. We had to isolate it from the bus start batteries and it's alternator.