I hope some of this info will help.
Most of this is based on using an Explorer 8.8.
1997 Explorer 8.8" 1967/70 Mustang 9"
Width 59.5" wheel flange to wheel flange 59.25" wheel flange to wheel flange
Springs Leaf, 39.125" on center with pads located below axle tube Leaf, 43" on center with pads located below axle tube
Brakes Disc 10x1.75" drums
Yoke Flange type u-joint mount Strap type u-joint mount
Tube Diameter 3.25" 3.25"
Splines 31 spline 28 or 31 spline
Shocks Mount to bracket on lower spring plate Mount to bracket on lower spring plate
Wheels 5 lug on 4.5" bolt circle 5 lug on 4.5" bolt circle
The Explorer also had a .75" diameter sway bar that can be easily adapted to the Mustang. It also had a 3.55 to 1 ratio gear set and limited slip differential.
The main changes that will need to be made are as follows. They shouldn't be to expensive or difficult:
? Move the spring pads to the correct location.
? Adapt the driveshaft to the flange style yoke.
? Adapt the brake lines and parking brake cables.
Couple things for the 8.8 Where I am they are pretty easy to find, I just sold one for 125 bucks drum to drum. They came in several cars from the Mustang to some Broncos so they are also pretty plentiful if you know where and what to look for. You would have to weld on some brackets for leaf springs and take off the brackets for the control arms. I am pretty much a tightwad so I have learned several ways around spending big money on stuff, and late model stuff is what I have been into the last couple years. The axles would probably have to be custom if you get the rear cut down. For the Ranger axles to fit in a late model mustang rear you have to get two driver side axles, the two sides on rangers are different with the passenger side being shorter (Maybe those would fit a cut rear? Might be worth checking, I have no clue) If you decide to go with the custom axles they cost around 400 bucks, I am not sure what all this includes but they are 31 spline. If you want a cheap 31 spline setup look for an explorer with a V8 or an expedition or some other truck they have a 31 spline Trac-loc, if you can find one with gears they come with 3.55s stock. I have a friend that was selling one for 150 bucks with no gears but decided to keep it. Overall if you go with an 8.8 it will probably cost a couple hundred bucks less than a 9 inch, that's if you go with someone else putting it together for you like Currie. Also instead of getting c-clip eliminators for the 8.8 I would probably weld on the 9 inch tubes mainly because I have heard of several people having problems with them leaking gear fluid. I don't know much about the 8 inch so I can't really comment on those. For disk brakes on the 8.8 you can get some off a Mark VII rear which I see in the yards all the time or you can get some off a 94+ mustang which are better brakes but also cost more. Many cars came with higher gears stock, the later trucks came with 3.55s the 87-88 Thunderbird TurboCoupe (which are rare around here) came with 4 lug axles 3.55 or 3.73 gears (depending on tranny) 4 lug disk brakes and 28 spline axles. The Mark VII came with 3.27 gears disk brakes 28 spline axles and 5 lug. The TC and the Mark VII housings are the same length as 79+ up mustang housing but the axles are .75 inch longer on each side. Hope this helps.
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65 coupe,351w,C4,Big Boss 429 hood scoop,8"3.40 TracLoc,Cragar SS,Black Suede.