You will be better off using a 3-wire Delco (10SI series) alternator. Will cost less, charge better at startup and is less likely to run down the battery if the tractor is not started for long periods. Also will properly operate your idiot light (a 1-wire alternator will not).
Wire up the 10SI as follows:
- Large wire to the alternator BAT (output) post
- Relocate wire from the #4 terminal on the old VR to the #1 aux terminal on the new alternator.
- Connect a jumper from the new alt output post to the #2 aux terminal.
Cutoff/tape all other wiring at the (unused) VR plug.