DM:
I've been thinking about this for few weeks now...
My solution is:
Get an F-150 rear end for '97-04, pull the axles and have machine shop redo the studs for 5x4.5" pattern (you will want to get the rotors done at same time). Adjust spring /shock/sway bar mounts from F-150 to Ranger positions while axles are getting drilled. The '97-04 F-150 differential is more/less the same width increase over the Ranger stock axle as the F-350 dually differential is compared to the single axle.
While you are at machine shop; have them make 4 adapters* to go from 5x4.5" pattern to 8x6.5". (For your solution, they can be Al 6061-T6).
You will also want a couple 3" - 8x6.5" pattern spacers for the front (probably best to purchase on net, machine shop probably can't match price for a one off). Normally, I wouldn't recommend stacked spacers, but in this case you are going to a larger bolt pattern and you will be using a rim with huge offset (load will be back to stock location more/less).
With the above setup, you can use stock Ford/Dodge 16x6J dually rims for all 6. Just instead of the 215/85R16s on an F-350; 215/60R16s (matches the stock 235/75R15s on my '98 4x2; ). For stock dually rims, you are limited 215**, maybe 225, otherwise you don't have enough space between rims for the tires to compress/squirm without contacting each other. For 4x4 tire choices are scarce - all the choice are E rated, and ride would be a little stiff.
*You don't
haveto do anything with the fronts, my solution is designed to have all 6 rims the same, so you only need one spare. You could probably get away with just a spare for the front - the odds of 3 tires on back failing at same time are remote (If 2 on one size fail; you take one off the other and install it, and start looking for a tire store fast
)
**Again you can put a spacer between the rear rims along with longer studs to use wider tires for which there is more selection, but stacking spacers on rear is risky - when you bounce up on the curb, all weight of truck is momentarily on the outside tire. Another alternative is if you can find 15" rims with the same diameter section as the 16s, you could cut the centers out of the 15s and install the 16" centers which would allow much greater selection.
My sandwich maker would probably be happier if I did this rather than continuing my pursuit of a tandem. I think the above solution is both possible and safe (not the cheapest though).
Let me know what you think.