The forward flipping gas cap aside. I am not a /5 guy. I don't own a /5 but I bought this tank that came off a /5 because it had stick on emblems. The seller was in total sympathy with what I wanted but he had no /6 bike to try the tank on. So I got a tank we think was original to this /5 and it doesn't fit my /6.
I have tried to bang the under side of this /5 tank with an air hammer and the longest blunt attachment I could come up with. It is not long enough to reach as deep as needed. My next plan is to try a Porta Power hydraulic body tool with the spreader attachment. I am going to make this tank fit some day if it kills both the tank and me it will fit on my bike.
BTW, this tank had an Aluminum gas cap so I really didn't loose much. The Aluminum gas caps can go for more than the tanks almost.