This clearly states that it works with 64-66 GMC.
http://www.classicparts.com/1963-Tur.../#.VpGNTOlIg5s
I have never seen a switch that included bearing and horn contact. But I haven't seen everything.
Please explain what exactly does not fit. What can not be transferred from old to new. The switch does fit 64-66 GMC as stated by the vendor if you have a 64-66 Stock GMC column to begin with and has not been modified or is not Chevrolet, etc.
The cancellor and upper bearing are sold separately.
http://www.classicparts.com/1960-66-.../#.VpGRA-lIg5s
http://www.classicparts.com/1960-66-.../#.VpGQwulIg5s
WHEN A BRAKE LIGHT FILLAMENT IS BURNED OUT IT IS ALSO THE TURN SIG AND WILL NOT FLASH AND SCREWS UP THE WORKS
That may be your only problem.