Measure your tire height from the ground to the top of the tire, use that measurement.
Definitely did not have disc brakes in the rear from the factory - probably was swapped in from an Explorer. Cool! That's a nice bonus.
If you don't have tags on the axles, you can pull the cover and count teeth on the ring & pinion, then divide the larger number by the smaller number... for example 41 ring gear teeth and 11 pinion = 3.73, 41 and 10 = 4.10 and so forth... the ring may even be stamped with the ratio. Dana gears usually are stamped with something like "41 11", not sure about Ford gears. Probably wouldn't hurt to take a look inside anyway given the sad state of your front end.