I believe the Delco relied on the springs to limit the total advance (up to a point of course) where the IH always used a slot in the lower plate to stop the total advance. So, the Delco could give much more advance say on an H than on an M due to more rpms. I also believe they were pretty long on the advance and if you have domed pistons or fire craters it would be totally wrong under load. Engines that don't use vacuum advance or computer controlled spark advance always sound to run better when they are over advanced while not under load. Just saying.
I never stand on my head to replace points etc on a IH distributor because it is so simple to take them off so you can properly clean up the advance and adjust the points so they align properly also. Always need to be retimed when you change points anyway.