Eric,
what is the material that you are using to extend your rear section, plastic or rubber? Are you going to use fiberglass to smooth out the transition between the existing tail section and the new piece. It will be interesting to see the results.
In '02 we made up a new tail for my Busa after running to the NAPA store to get some plastic mudflaps, tail length in the modified class was being enforced and I was too cheap to hack up the tail like everyone else. Lots of duct tape, passed inspection with it and made it to impound.
Cheers,
Scott