Quick question:
With that Rancho lift for a 04 FX4 Supercrew, can I put aftermarket coilovers for a 6" lift on the 4" Rancho lift (i hear it is 5", anyways) and achieve a 6" lift? How will that affect the geometry of the suspension?

 

I wouldn't do it. I'd go ahead and get a 6 inch Fabtech or RCD lift instead.

 

the rancho lift is a 4" & if you tried to put some 6" coil overs on it it would cause a bind on all your suspension components & c.v.s & cause them to prematurely wear out & it wont be covered by your ford warranty