Brian, with three terminals you should have your battery connection, large post, small terminal which goes to your start terminal on your switch, and then you would have your other large post which should crank over your starter. If i am thinking correctly you should be able to hook up your power for the coil during starting to the post that powers the starter. Typically that is what the other small post or fourth terminal is for. Then when you release the switch back to the run position it should by pass the solenoid and run your coil from the key switch.
Correct me if my thinking is wrong guys, but that is what I would do if it were on the starflite.
Good luck Brian I hope it works for you.
Oh, make sure you check the number of teeth on the bendix on your old starter to make sure your new starter matches, or you could end up replacing the flywheel!