1974 GMC 2500 L/B ????'s

[dhocpatc]

Hey everyone. I am new to this site. I recently purchased a 1974 GMC Sierra Grande 2500 3/4 ton long bed pickup truck and I have one major question.

The ORIGINAL engine in this truck was a big block 454 but when I got the truck, the engine had already been swapped down to a 350 for better fuel mileage.

The only problem is that I do not know what year or make/model of vehicle that this 350 came out of so ordering parts for it is making it hard.

How can I find out what year and/or make/model of vehicle that the engine that is currently in my truck came out of?

Also, I have another bed to put on this truck because the one that is on it is starting to rust out around the wheelwells and also the front end really bad, but the only thing is that my truck is equipped with dual tanks and the bed that I have is only equipped for one fuel tank. I have not used the tank on the right side the entire time that I have had the truck and I was told that the tank on the right side did not work anyway. Since I do not use the tank on the right side, can I just drop the tank completely and remove the switch inside the truck that switches the tanks so that I can use my other bed that only has a place for the single fuel tank on the left hand side of the truck?

Thank you for taking the time to read this, and i look forward to your help!