Push button for what?

For the countershaft brake? If so then there will be something more than a cover plate bolted on a PTO opening, it will be one casting generally flat and have a second casting about 3" square and a small air line going to the middle of it.

For the range shift? Yes, it should have a valve in the shifter knob or one hose clamped to the shifter stalk, I can see the range air cylinder in the transmission photo, top right when looking from the back.

Grigg

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
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"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-