Have a 56 ford want to install a ford 9", with a heidts 4 link with a little mini tub into box. Hoping for some help on how to measure to shorten the 9" axle tubes .

 

I did a 96 explorer 8.8 rear....3:73 position and disc brakes, they can handle good horse power, I scored one out of a junk yard for a hundred bucks

 

There are a few unknowns in your statement...do you intend to mount the 4-link inside or outside the frame? Do you have a wheel/tire size in mind? The frame is 34 inches wide, the box is around 49 inches in width. This gives you about 7 inches on each side of the frame to tub out. Combine that with 10 inches of fender opening and you have a fairly sizable 17 inches on each side for tires. Here is a diagram I found from Art Morrison that may help:

 

Charlie,
Thanks for the diagram

 

Do a triangulated 4 link

 

how's the fitment? spring perch to spring perch measurement? i've got one from a F150, but it is a bit too wide... sounds like the exploder 8.8s were narrower (and of course discs!).