Alan,
Entry noted for John English.
Eddie,
ultimatecarpage.com give the overall width for the Shelby T10 King Cobra as 65inches which scales out to 51.6mm.
So I'm going to say no to running it in the pre 68 class but if you want to use it in the Can-Am class that will be OK.
Hope you understand.
Cheers.
Mick.