The filler neck connecting hose is no longer available. I found a company that makes a reducer for 1 3/4 in. hose that matches the 1 1/2 in. end of the metal filler tube. The part is made for fuel, and it installs in the end of the hose, then (with a little lube) is pushed over the tube. I am in the process of swapping tanks, and it fits perfectly with a 4 7/8 in. piece of 1 3/4 inch tubing also available from them by the inch (minimum 1 foot).
Filler Neck Supply Co.
10020 E Montgomery Ave Bldg 2
Spokane Valley WA, 99206
fillernecksupply.com
The part number is B03.