Most mustangs are 28 spline. The only 31 spline mustang chunk that I am aware up up to '04 was the '03 & '04 Cobra and those used better carbon fiber frictions.
Explorers & F150s should be 31 spline and therefore be more desirable than all mustang chunks but the cobra. The truck diffs used standard frictions but an FRPP CF friction rebuild kit is only $120 or so.