Charles,
Sorry to hear about your motor – I’m glad you got it fixed, I think that I saw your name at the last IMI race?
The rear width is 55″, but you will not run that wide at most of the tracks in colorado. You run a birel chassis so you might ask a few of the guys that run birel for their setups at some of the tracks and move on from there. At IMI I run the rear pretty narrow – around 52 3/4″ with the front about 30 mm out (medium). The best thing to do is just take your kart and practice. I am planning on getting out there at the beginning of the year and try and find some other tags to run around with.
Good luck next year.