SBG...
Yes. I agree about the Rancho. If you have fab skills, you might consider making your own custom drop bracketry (especially since it would not fit the new diff anyway). The kick in the teeth however, are the knuckles and the torsion bar extensions. These pieces are a big part of why the Rancho kit works so well. They are cast items and it would be nice to get them from Rancho, to save the hassle of engineering and building them from scratch. And Yes...Rancho shocks are awful.
I think a late-model GM 1/2-ton IFS is a great idea. But, like you say...its on the wrong side (yeah I started there). That in itself poses some huge problems, because the H3's t-case is so specialized. IMO...the 4494 t-case is what makes the H3. Without it...you might as well go buy a Jeep. I'm not sure you can "clock" the 4494 t-case like say...an NP205. It has a fluid pump, a sump, and some "juicey" stuff inside it that may prevent you from rotating it. So if you are going for a driver-side drop on the axle...you should probably swap in a different t-case as well. That means a host of dash-lights, electronic gremlins, and giving up the 4:1 low. The nice thing is that if you swapped in BOTH the full-size IFS and the matching t-case...you would be able to add a 2WD button to the dash. The full-size axle already comes with a CAD solenoid, and you would have to wire that up to function with the t-case. It would be a helluva project for sure...but I would love to see it done. I think you can get a 4:1 kit for late-model full-size transfer cases, to retain your trail-worthy-ness.
Or just go the easy route..bolt your H3 body onto a 2012 salvage full-size chassis. This way you could get a Duramax, a 6.0L gas, a stick-shift, an Allison 6-speed, 3/4-ton axles, etc. I'm not joking...I seriously think it would be easier. And the final result would be twice the truck (Bully-dog).
Ford 9"? Nah. That stuff is for tubbed Camaros & 18" wide Mickeys.
BCIL...True on the FJ's. The front frame rails are prone to stress-cracking as well. I don't think any of the manufacturers (including Jeep) build their stuff for 35"s and extreme wheeling. All of these rigs are becoming dinosaurs, and soon we will be able to pick them up for very little money. Who wants a ten-year-old H3 with a broken front axle and a bunch of check engine lights? I-do! I-do! Plasma and welder standing by!