Rebuild on 300 Cummins

Personally I'd just roll bearings in, dropped maybe 5 numbers on the button, back off the AFC adjustment a little bit, and shim the idle spring enough to give you about 2500 RPM high idle

Buttons are cheap and easy to change, if you think dropping five numbers is too much or not enough you can always change it a few numbers either way.

Go online and look for Cummins idle spring plunger, that's technically what the button is called. Last time I bought them I think they were maybe $10 each. The lower the number the more fuel it's going to inject. They're under that little cone on the back of your PT pump, the one with the plug on the end of it that you take out to adjust your idle speed.