Sorry for the delay, I finally got back to measure the track on my CR I. The front body width is 68". The front track is 58". My '90 Mustang (drum config) 8.8" rear is 58 1/4".
I have a set of Halibrand style Cobra II pin drive wheels that I plan on using. The 7.5" X 15" front wheels will fit fine. My rear 9.5" X 15" wheels with the 1/2" added pin adaptor will stick out about 1/2" beyond the rear body. But the Firestone Firehawk Indy 500 tires I plan on using will still (just) tuck under the fender due to its shape.
At worst case you can select a different offset wheel and get the rears to tuck under the fender. I have a set of 17" X 9" ET style wheels for a late model Mustang that I test fit to my CR I and I would have had to use 2" spacers to set the outer edge of the tire to the edge of the fender. But the wheel still cleared all of the body & frame inside. With your wider rear end it would place the wheel in just about the right spot!
Thom