'61 Dart axle

[Tim Exley]

I need to know the correct length for a rear axle for my '61 Dart. I will be running 5" Tri-Stars on it. What would the rear tread width be? How is it measured? I've heard two opinions. 
Also, what is the front tread width for a '61 Dart? Thanks

[Tom Bowman]

A Rupp ad I have says tread width is 31" front / 32" rear. This is what I used on my A-Bone. With Rupp Grand Prix wheels a 34" step to step axle gives you the 32". Tread width is measured from center to center of the tire.