btmatt, after installing mustang gas tank in your 57 chevy pickup truck, what filler neck was used to connect to gas tank and accept a gas cap
Fire Chief, To be honest, Life has happened and I have not had time to mess with the truck lately; hopefully the new year will shine on me and I will be able to find some garage time again. My plan was to cut the neck off of a B-body GM (mid 60's vintage) and re-work to fit. Back-up plan was to have something bent at the muffler shop and re-attach the the filler ring from the original neck.
In Mustangs and Falcons and Fairlanes where this style tank is found the filler neck is a separate piece that bolts into the back panel of the car between the taillamps. It is connected to the tanks by a short piece of gas filler hose held by two clamps. If the tank is easy to remove where you are using it and the filler neck would be no problem it would likely be best to weld it to the tank rather than use the connector hose.
Go to the Tanksinc sice and look under the acceresories. They should have what you want. Todd http://www.tanksinc.com/index.cfm/page/ptype=results/category_id=62/home_id=62/mode=cat/cat62.htm