[LH Lead-Foot]

Well, even with all of the original information provided by the Delco Carb Book #9 which I spent 3+ hours looking thru, here is what I can tell you.
The carb number does not appear in print, but is not uncommon, it does indicate it is a 1972 monojet for the 250 cu. in. engine. (Photos below)

While the choke is controlled by a choke stove and linkage and did not use a cable. (Photo below)

The "Green" wire is generally hot with the key. It controls the throttle stop solenoid that is used to adjust idle speed when warm. It drops the throttle closed when shut off to prevent "Dieseling or Run-on". It is adjusted for correct idle speed after correct timing and air/fuel is adjusted and the engine is at temp.

The "Yellow" solenoid was a mystery until my Detroit GM buddy came back from vacation. He indicate that the Muncie 426 manual trans came with variations that included up to 2 "PTO" plates to add pumps, drives and other things that could be added at the dealer or an outfitter for a dump flat bed application. It would be adjusted to hold the engines RPM speed desired for PTO operation for what they installed.
Many kits where sold with Delco parts, wires, switch and etc. at the dealer, but installed elsewhere. The PTO would be operated or engaged with a large knob choke type cable to the gear box on the tranny. A switch would be added under the dash that raised the engines speed for hands free operation of the power-take-off device. It could be removed without effecting the carburetors operation. Bobby G. has been with GM since 1972 in various capacities.

Yes, while it true that many manufactures used a 4th gear switch to retard ignition timing to prevent ping or knock (Even Imports) when using small 4 or 6 cylinder engines. Bobby G is positive the solenoid was for PTO operation.

Check it first to see what it touches. If it pushes on the throttle in such a way as to open it when energized to raise the engine speed, that is what it was for. It is hard to tell from the photo's you posted. Due to it's size, it will push hard and is designed for long continuous operation. If one wire, it's ground thru the body. If two wires, well the ground and positive both are required...but it is optional GM equipment and somewhat a rare find.

If it works this way, as I said it could be removed. Someone out there may want to buy it to keep their truck original when equipped with a PTO device.

My 67 C10 came with this tranny, while in first gear, you could get out and walk faster than it moved. These where built like tractors with a cab on them.

Best of luck. Hope this helps.