My 68 D100 also has the tank behind the seat & I have a fuel cell that
we were going to place inside the frame, under the bed, but think we're going to add a return line to the stock tank so I can finish the resto & get the truck up for sale. The gerotor design pumps are the quietest I've heard & the Holley 150 gph one I had on a Hemi Challenger years back was just as quiet as the Mallory.
I just worry about having a return plumbed into the cab with pressurized fuel...just doesn't sound safe to me. To a rear tank...no problem.
