A total of two inches of slop at the wheel itself is not only not uncommon, it's actually pretty tight! Depending on the size of the wheel this is just how older vehicles were for the most part.
Sure, some performance vehicles were tighter and also had quicker boxes with as little as 2 turns lock-to-lock, but most trucks of this vintage did not. Maybe there is a replacement box out there with zero play, but I've never seen one.
How big is your steering wheel? Stock size, or smaller? With a really small diameter wheel I can see that 2" being kind of annoying. But with a stock size box I'd consider that good and tight.
And frankly, with zero play in a vehicle like a Bronco most driver's would be hating it for being twitchy and over sensitive. You may be one of those that is super steady with your hands while driving and maybe it would be a great thing, but I'm still betting that most people actually benefit from that slight amount of free-play.
A loose or worn out gearbox of this type would have more like 4" of extra play up at the wheel. Again, depending on the wheel diameter.
But assuming that you've done all testing and the only slop left in the system is the box itself, maybe converting to something out of a more modern vehicle from the late '90's or newer would be the ticket. Won't be easy, but it "might" be one possible solution.
Maybe someone that has done the 4x4x2 conversion can give us their specifications on play. It's an older 4-turn box, but utilizes the input section from an '80's and newer Ford box. Maybe they're tighter than what you've been finding.
I doubt it, but since I haven't played with any that much I'd still be curious what others' experiences have been.
Sounds from your description that the boxes you've tried so far are the brand new ones with 4-turns (or less?) lock-to-lock from the Bronco vendors? New and not rebuilt, correct?
Rack-n-pinion is tight, but would be super awkward to fab up. I think it's been done, but not often.
And just so you know for sure that 100% of the slop is in the box, and none of it is being added to it from the other components having a tiny amount of play that adds up, have you done the test with the vehicle on the ground and a helper turning the steering wheel back and forth about a half-turn in each direction?
Not only will this highlight the loose box, but also even tiny amounts of play in trackbars, ball joints, wheel bearings, and even the cracked frame mentioned before.
Sorry if you've already done it, but it's still a great test and worth mentioning.
No matter which way you go, good luck with getting rid of that last little bit.
Paul
