So your driver side tank filled through a door and not higher up on the bed with an exposed cap like on the cab? If so, either some body work was done or you have an aftermarket tank. No matter, they all sit the same. I've never had tanks on a coil spring truck, so don't know about differences. But, any leaf spring truck would be the same tank. They were only available on longbeds.
First one is '72 factory option and second s aftermarket. Best pics I have to show. I hope you can see.
Man, had the exhaust done on the GMC in '04 and hate how they did the mufflers turn sideways hanging down so low...stupid. Gonna see about changing that soon! (finally)