Thanks to everyone for ideas and learning experience.
Tractor starts and runs fine. Time and time again. Brother also now has working lights on tractor - first time in about 35 years. He's a happy camper.
Cause of his problems as determined and corrected thus far: 1) Ignition switch was erratic, 2) bad feed-thru on primary at side of distributor.
All advice was welcomed; but perhaps best advice was to hot wire the thing. By pulling power to the coil directly from battery cable at the solenoid I was able to isolate, identify and correct that part of the problem. Then the next problem was isolated, identified and solved rather quickly.