https://www.dippy.org/forum2/index.php/topic,209.0.html
Is a good source for leaf spring details.
Note: Changing differential does not directly affect the leaf spring usage (or vice versa) - with one minor detail/exception.
The differentials that use Iso-Clamps have a bigger hole to locate itself on the spring pin. The Iso-Clamp cars, the hole is (I think) 1-7/16” (but might be off). The pre-IsoClamp differentials have a ½” hole (again, I think – but might be wrong).
It is not too hard to make differential perches at 1-7/16”, if wanted – but personally, I highly recommend tossing the Iso-Clamp system as far as you can toss it. The pre-IsoClamp shock plates are easy to find, a lot less complicated, less prong to failure and will make car handle so much better.
If using a FMJ differential and using the older shock plates, then a person will need to find or make something to fill the 1-7/16” hole with and weld it into the existing holes. Then drill a ½” hole in center of your gap filler.
If using a ’65-70 B-body differential, elongating the holes 0.22” outwards, per side – will do the trick.
I have discovered that spring flex will allow you to install a ’65-70 differential without any modifications at all.
Matter of fact, a ’66-70 B-Body Dana 60 will bolt right in place – if a person wanted something stronger (and had a lot of extra coin burning a hole in your pocket).
Just keep in mind that propeller shafts are different lengths for no matter what differential you use (ie: 7¼” prop shafts are longest, 9¾” (Dana 60) would be the shortest, 8¾” next shortest, 9¼” middle length and 8¼” second longest).
I don’t know how the Ford 8.8” falls in there – but a safe bet is you’ll need a different length shaft than what you currently have on hand.
BudW