You could not get the 4x4 dually of Ford untill the 99 superduty (extended cab and crew cab). Only cab and chassis 4x4 dually's in Ford till 99. If you see otherwise they are conversions. Either by the individual or by companies such as Centurion.
The hitch should be adjustable for height. If not you could do it yourself either via trailer or truck hitch. The trailer should not hit the bed or rails 4x2 or 4x4.