rule of thumb is you can go 2" up or 2" lower on your stock shocks. Nobody has reported running taller shocks up front because of the torsion crank. Plus those shocks don't exist for the front either.
All 98+ 4x4's sit the same with the exception of 08+'s which are lowered from the factory compared to 07 and older models. A shock designed for a 98-07 4x4 will be just fine with your truck. Maybe a little longer for the rear though. Up front you really have no options for longer, taller shocks other than a Superlift shock that comes iwth their 4" lift kit, which will be far too long for your truck.
'01 XLT disguised as a '03 Fx4 Level II
Big. Loud. Slow. Bright.