If you want to get serious about this, these are the people to contact https://ptggear.com/
I've though of this for a while, but the issue is that their are primarily two camps of people that want these rear axles and different ratios.
1, us, the guys that would like some more highway friendly gearing (3.30-3.70ish sets)
2, rock crawler and mud bog guys that want to find the elusive 5.83 sets and would probably want custom 6.17's or something
Getting a custom set made is possible, but I haven't gotten any quotes yet.
The biggest financial issue you will probably run into is that you will probably need a few thousand sets made to get the cost per unit low enough for people to consider buying a set. Then you have to wonder about how many people would actually buy a set.
If I was independently wealthy, I would totally make some 3.50ish sets and sell them for cheap <$500 to whoever was interested and just take the financial hit because I love these old trucks and would like to see more of them used for everyday driving, but I'm not.