You'll need to figure out where your at now by measuring the length of your current coils compressed (if you have spacers in there, you'll need to account for those at the same time). This will be the height you need to shoot for with the new coils (adding or subtracting whatever amount needed if you're also changing your lift height).
With a 4" lift, you're probably somewhere around 14.5-15" compressed length)
Figure out how much weight you have up front minus the axle & tires, divide that by 2 (two springs), multiply that by 1.5 (TTB leverage effect), and finally divide that by the PPI rating of the coil to get how much it will compress. Add that amount to the figure you got from your current setup to find the free length of the coils you should be looking for.
As an example:
For a Supercab weighing 2400lbs up front (subtracting 300 for the axle & tires) and using 300PPI coils on a 4" lift...
2100 ÷ 2 × 1.5 ÷ 300 = 5.25" the spring will compress.
5.25" + 14.5" = 19.75" free length 300PPI coils you'd need.
IIRC, the Superflex EARLY Bronco coils you linked are pretty soft, like 200PPI. I think something in the 275-325 PPI range would be better on a Supercab truck.
F-150 Superflex coils are 300PPI and might be what you'd want to use. They're pretty long though so you might need to trim a winding or 2 off them to get it down to 4" lift on your Ranger (which will stiffen them a bit, though not by a lot).
The other option is
early Bronco standard coils together with a spacer which might work better for you.
Hopefully that helps some.