The first service truck that I had, when I became a field service technician, was an ‘86 GMC 3500 with a 454, 4 speed, and 70 gallon LP tank in the back. It ran on gasoline or LP. On LP it would run really smooth, but didn’t have as much power. However, you could lug it down quite low without the chugging that you’d get on gasoline. In the winter months you needed to remember to switch back to gasoline before parking it for the night. If it was too cold in the morning the LP regulator couldn’t provide enough LP gas for the engine to start. Once started on gasoline, and warmed up, it could be switched back to LP. Engine coolant ran through the LP regulator to keep it from freezing.
And in regards to your carbon comment, you are right. It burns much cleaner, but spark plug life was much shorter. They seemed to deteriorate quicker.