Rear end width?

Crackedback, thanks for the tip. It makes sense and interestingly I was thinking of making the rear about 1/4 " narrower on each side just to give a little more clearance to the outside. The Darts are not that easy to slip a wider tire into. The rear I have was under a 30's chebby truck, so I was going to place the spring perches where I need them.

I appreciate the help, it's a lot easier to do it right the first time then to figure it out from your mistakes.