the most important timing angle is measured at 3000 rpm vacuum disconnected (simulating full load) because that's when if you have wrong timing you can do damage, don't worry about idle timing.

I think it should be between 18-22 degrees (3k vac discon.) for a 1972 us model M117 engine

page 2 of this pdf has more info:

https://www.startekinfo.com/StarTek/outside/11883/PROGRAM/Engine/107/M117_45/075-500.pdf