Yep CR's don't have much dish on the wheels. It's something Ian improved on with the round tube chassis.
That being said it's possible to modify for more rear dish but it's a lot of work.
Some years ago I designed and built jigs to make new rear arms in different lengths. A couple of people have used them now. Paul Trefry has built an amazing looking traditional styled Cobra after making new rear arms. I'll see if I can find a pic.
Here's the new rear end
Here's a before and after shot of the rear dish on mine. (Look out, It's Ben Hurr)
And here's the after with about 2" more dish
I would probably advise against this as you will end up like me and be forever modifying and changing things and never bloody driving the thing.
Phil Mizzi has achieved a great traditional look with 15" rims on the Orphan without narrowing the rear end. It needs some careful work with getting the right wheel offsets.
Cheers