I recently came across a few websites of a guy the converted IMAX 2000 antennas as well.. He makes them better, but can also retun them more bands.
Links to his websites are below.
I think the page you can check out his CB antennas are: http://www.bighairantennas.com/CB_Antennas.html
And the page, that shows how he converts and upgrades an IMAX 2000 Antenna: http://www.bighairantennas.com/BigHairsAntennasversuscompetitors.html