If you strike out, maybe a machine shop can make you one.
Another question, who makes your wheels? On my truck they are aftermarket steel wheels made by Rockwell International.
I'm not sure if anyone makes an 8 to 10 lug adapter. What bolt pattern are you after? The OBS F-Superduty rear ends are true dually rears and use 10 lugs. I believe you also gain rear disc brakes and need the master cylinder and goofy parking brake set up to go with it. Plenty of posts about this you can search.
If you have stock DRW wheels then getting a true 2WD DRW rear out of a 95-97 (other posts claim an improved yolk/pinion in 95) truck, it should pretty much be a bolt in. Maybe parking brake cables are different due to 3.5" wide drums vs. 3". Then use salvage front adapters off off an OBS 4x4 chassis cab. You are then all factory parts and have less headaches on weird conversion parts. You just have to remember which year/model to tell the parts guy what to look at for your Johnny Cash inspired 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59 year model truckomobile. And hope you never find a dealer parts guy who is paralyzed without a VIN number.
In reading your other links I thought I'd give some more info. On Centurian, Roll-A-Long and CNS Vehicles Inc., Ford sent the truck directly the converter who then shipped it to the ordering dealer. It's called "ship-thru" and is the same thing that is done on custom vans and all means of body upfitters. Ford has a huge list of approved upfitters and you can read more here: https://www.fleet.ford.com/truckbbas/index.htm
In many cases the Ford warranty covers everything. You buy it as you want it from the dealer and their service department fixes it but it may be made with aftermarket parts.
How do you spot one of these DRW conversions? There are several dead giveaways. One is the upfitter label on the drivers door jamb. Another is the factory vehicle data label. Every professional conversion I've seen started with an F-350 SRW crew cab 4x4. A crew cab 4x4 SRW has a GVWR of 9200 pounds. A factory 2X4 crew cab dually has a GVWR of 10,000 pounds or so. So if factory data label shows 9200# it started life as a SRW. The pic of the white XL truck in one of your links shows non DRW wheels on the front. This is the cheap way to convert a truck....just bolt on fenders and rear wheel adapters. Only individuals did it this way. The other thing is to lay on the ground underneath the bed and look at the fenders and how they attach. A factory DRW bed has a huge amount of metal cut out around the wheel opening. A converted truck will just have holes drilled thru the regular bed. This causes another headache if you ever need to replace a fender. Factory DRW fenders will not bolt up as the attachment is completely different. I found this out the hard way. Further complicating matters is there are at least 2 styles of aftermarket fenders. Mine, CNS Vehicles Inc., have about a 1" lip on them that allows installing the rear wheelwell moulding off the SRW trucks. I have seen one Roll-A-Long conversion with a lip. Centurian and Arrowcraft fenders do not have this. I have found no source for the fenders with lip. The factory fenders also do not have a lip.
See my Webshots for pics of the fender lip. Don't want to post the certification label up as it has my VIN. Would be glad to e-mail it to any interested parties who PM me though. 1996 F-350 DRW 4x4 pictures from good times photos on webshots
'94 F350 4x4 PowerStroke, 5-speed, 4.10 gears, crew cab, XLT, Luk Clutch, ZF-47, Hydroboost, AIC, Max A/C Assist, 95.5 radiator and degas bottle 318,000 miles
'96 F350 4x4 PowerStroke, auto, 4.10 gears, crew cab, XLT, DRW conversion, AIC, 502,000 miles
'02 F350 4x4 PowerStroke, 6-speed, 3.73 gears, crew cab, XLT, DRW, AIC, 223,000 miles