Based on your abilities, I would pony up for the original alternator. Installing a different alternator is not an easy thing to do. You will need to fabricate a bracket to mount and tension it. You will need to wire the alternator. You will need to route a belt to it. Spend the money for a replacement oe alternator. Before you disconnect it, draw a picture of the wires. Note both the wire color and the terminal type. Consider using different types of tape to mark the connections. Now go to the battery. Trace the wire down to the connection. It will either go to the starter or the frame. Mark the hot wire with a piece of red electrical tape. Now trace it again. Do it a third time to make sure you have things right.
Does anybody know if this tractor has a fuseable link he may have blown?