does anyone know what the unsprung height of the 1988 f150 coil spring is?

 

There's a lot of factors that go into coil springs such as engine, trans, 2 or 4wd, ac, cab, bed and GVW. I don't know what your particular specs are but I can give you the specs on a typical factory replacement coil

Inside Dia.= 4
Bar Dia.=.718
Install Height = 12.13
Load = 1428
Spring Rate = 366
Free Height = 16.19