A100 ? That is a Dodge truck I believe. Fords start with E100. Anyways. The gas tanks are hard to find for replacements for our Econoline trucks and vans of those years. I read in other threads where guys have fittted in Mustang gas tanks and they need some minor mods to fit.
The other is to have your gas tank cleaned in a reputable shop. Or you split the tank open along the seam and get inthere and do a good wire brush cleaning. Syraighten dents and solder or weld holes. Then resolder the seam back together. Now there is a product out there that a person can pour in the tank before you put you floats and gas line back on that will line the tank with a gas resistant coating to prevent rusting and future leaks.
Read some of the other threads on gas tanks and see what some did with the Mustang tanks.
As for filler neck Only the ones from the Econolines will work. You need the proper hose that will not detiorate from gas. Rad hoses look like they would work, but by the time you do a 2nd or 3rd fill they have big rotted holes. So the proper neoprene hose is needed.