I've been trying to increase Goliath's fuel capacity for a long time now, without much luck. The IMS and Clarke tanks for the 2004 didn't work, they hit the head where the petcock came down. The IMS tank for the 2007 had the same problem. ZZ3GMC suggested the Clarke 2005 to 2007 tank, so I ordered one from justgastanks.com in black. It finally came in Friday and I had a chance to work on it today. It did not have the deep petcock area so it was much closer to fitting than any of the other tanks, but it did need some adjustment. I was having the most problems in the head stay area, which required both some grinding on the head stay and heat gun work. In order to spread out the pressure and not poke a hole, I made a cover for the area out of 2" PVC that I cut lengthwise so it would slip over the area. I would heat the area on the tank, and then put the tank on bike so I could apply pressure and hold it while it cooled. I slowly added some Gorilla Tape to make the PVC thicker, and re-heated the area. It was slow going, and the PVC piece had to be pretty thick with tape when I was done, but it fits really well.
Here is the PVC piece:
Here is the tank mounted:
All buttoned up and ready to go: