[vin63]

I interpreted the OP's question as what I did for original aesthetics (for a non-functional filler neck and cap)...not to use the original filler neck and route a filler hose from the cab to rear of the bed.

The original cap and filler neck was also non-functional on my '63 Chevy II Super Gas car (I had to run a fuel cell). I cut down the original filler neck nearly flush with the backside of the rear quarter panel and welded the bolt-in flange to the neck to keep it place since I was running such a tall tire.

Originally Posted by 62stepside longbox

If you try to route a hose all the way from the stock filler to the rear tank you will run into the problem of our trucks having lots of frame flex. If you're driving your truck on a bumpy road and look back at your bed you will find that it moves side to side a lot more than the cab. Even if you do use flexible rubber hose for the bed to cab connection I would still be worried about it getting cut or torn from the bed moving so much, this flex is the reason our trucks could never be unibodys. I would say just find a more era correct cap for the rear tank and be done with it.