If you found a complete propane system from a GM vehicle, then you should be able to install everything on your truck. Be sure to get EVERYTHING, including the control panel and cables from inside the vehicle. The tank is most expensive part of a conversion and other propane system parts are still available and not expensive. Like shown in the video, an Impco Model 300 mixer is commonly used on dual fuel conversions.

With vehicles last equipped with carburetors in the late 1980s, carburetor conversion parts have gradually become obsolete. The challenge with a dual fuel system is getting the timing optimized for running 2 fuels. Dual Curve used to make timing controllers for dual fuel engines but now timing advance processors are only made by AEB (AEB Wolf-N for noncomputerized ignition systems). You can also switch to a computerized ignition system for better timing control. See Megajolt/E.

Before converting your truck, you should make sure that you have a readily available supply of low-cost propane motor fuel (HD5). Often, propane companies offer fixed-price supply contracts and the cheapest price can be locked-in during the summer. Ideally, the price of propane should be much less than 50% of the price of gasoline to have a quick payback on the conversion.

If your GM conversion is mono-fuel, it would be very similar to the system to the one I installed on my 78 New Yorker which I later transferred to my 77 Pontiac. See Model 425 Mono-fuel Carburetion.