I believe (don't hold me to this) my rear fuel tank is a J.C. Whitney P/N ZX862180N 25 gallon steel unit. See:

http://www.jcwhitney.com/webapp/wcs...2B1984%2B600002073&c atalogId=10101

My front fuel tank is the original stock 16.5 gallon unit that I removed from behind the seat and re-installed at the very front of the Fleetline bed. I removed the original filler/cap, filled in the hole, and re-installed the cap/filler at the driver's side front of the bed. This setup gives me over 40 gallons of fuel capacity and weight over the rear wheels.

Hope this info helps.