Narrowed rear end question

[sacustomcycle]

I've got a 67 short wide and I'm getting ready to narrow the rear end on it. I would like to find out from those of you that have tubbs and narrowed rear ends, what is the overall width you have from outside of the tire to the outside of the other tire? My bed isn't together, so its hard for me to get an accurate measurement. I may have to bolt it together just to get the width.

I'll be running Sportsman S/R tires (33X22X15) on 15" wide wheels. On previous cars I've done, I took the fender width minus 3" and its worked out good.

I appreciate any info I can get and welcome any tips or tricks.