Actually, all gen 1 explorers came with a tow bumper. However, the optional tow package included a limited slip 3.73 rear, external tranny cooler for the automatics, larger radiator (super engine cooling), a wiring cable that connects under the bumper (stored in the rear with relays above the rear washer resivore), extra capacity rear springs. There might be some additional small things, but you could not buy or order a gen 1 explorer with any type of factory reciever hitch. If it had one, it was installed by the dealer. And no manufacturer provides a ball and drop hitch that I know of, since ball sizes vary so widely, that'd be silly.
Oh, and the rear bumper capacity is 3500 lbs, with a 500 lbs tongue weight. I've been jerked out of the mud by my factory bumper and a 2 inch ball several times, which would equal well over the 3500 lb limit (3600 lb vehicle stuck in mud probably adding another 2K lbs of resistance) and never even tweeked the bumper.
The tow capacity of my 92 stock with 3.27 gears was 1,500 lbs, so the bumper ball mount could pull far more than the drivetrain was rated for.