There was a post, not sure if it was on here or the old site, that had a procedure for expanding the OEM tank.
Don't quote me but I think it was:
empty tank of all gas
keep tank on bike & plastics on tank from here on out
Fill with boiling water
let sit (for how long I can remember)
Put a modified cap on that will allow you to pressurize with compressed air (usually a tusk z400 aluminum one with the rubber bladder removed should work)
Blow up the tank with compressed air and hold until tank is cool enough to hold the new shape
Drain all water
refill with gas & use
**leave plastics so new tank shape will adhere to plastics otherwise the plastics will not fit
Maybe somebody has the link to the old post for more exact details