Was thinking of removing a foot or so off the back end of my 77. In doing so, i was also hoping to get rid of the factory tank all together and run a fuel cell. Do i need an electrical fuel pump to do this or does the factory pump ( running off the cam ) work. Thinking about a 20 gallon tank mounted through the bed and resting on the frame.

nothing special about the tank in a 77. The engine mounted fuel pump will work hooked up to pretty much anything.(if it has fuel in it)

Great news. I wanted to run a jazz fuel cell. Thanks for the info.

You could still run an inline electric pump as a backup incase the mechanical pump fails.