For an '86 the cheapest way to go 5 lug is 1st generation Ranger 4x2 front brake rotors and the standard Ranger rear axle conversion all Fox's can use.
'79-'86 Mustang 4 lug rotors use the same bearings and are the same diameter as the '83-'88 (for sure, through '93 as well I think) 4x2 Ranger. Th eonly difference is the 4 vs 5 lugs.