I don't think the early box is a stronger box, I think he meant it provides more boost. Which is what 4xBob referred to. I agree with 4xBob -- the early boxes have too much boost, and zero road feel. I much prefer the later boxes.
There is one additional difference. In the later years, all the steering boxes have a 14:1 ratio. In the early years, the stock ratio was 14:1 but the off-road package used a box with a 17:1 ratio. I got one of those when I put a used box into my '88 Comanche.
It sucks. In addition to being over-boosted like all the early boxes, it also adds almost a full turn of the steering wheel when going from full left to full right.