The nuts are .465 inches tall.
They also are identical to the top retainer nut EXCEPT for the nylon portion. In other words - if you grind off the nylon insert section, you would have the same nut as the lower retainer nut
Also, no Ford dealer had these in stock in Michigan - 1 day ordering to get. And they cost $8 each.
Either plan ahead or go to plan B (junkyard) or plan C and improvise your own.
One last finding - as theorized above, it was possible to remove both of the nuts with the spring/strut still in the car. That's what I did at the junkyard, and the strut never moved.
Scott