I just replaced the tank in my ’66 without touching the clamps on the filler tube. All I did was spray some lube on the seal ring on the cab, removed the gas cap, disconnected the gas line and electric, removed the two bolts (after spraying them generously with WD40) and by lifting the passenger side all the way to the top front of the cab and twisting it slightly I maneuvered the neck right out. I put the new tank back in the same way, but needed a little help to guide the neck back in why we twisted the tank. Just make sure the seat is all the way forward. And as Tony said, make sure you take most of the gas out of it first.
