gd,
From the cab, turn key on, press pedal to floor and start.
From the engine bay, have someone get in cab and turn key. You should see the brass bolt extend to touch the throttle lever. Press back on the throttle lever and the brass bolt should follow it.
Or take a hot wire, disconnect the connector on the solenoid and touch the wire to the spade on the solenoid. The brass bolt should extend.
That brass bolt is how you adjust it also.
I had a crazy thought in the past that an idle stop solenoid off a carburetor could be swapped in there. They're used to fully close the butterflies on a carb so that newer, better, leaner running cars wouldn't diesel on shutdown. They might also be used to kick up idle with the AC on. You can get one of them for about $50.