Good to see you found the other threads on big wheels Thor, I was going to link them but you found them on your own. One thing I wanted to suggest was a Yamaha Big Wheel swing arm, I'm not sure if you're familiar. They have a jack shaft so you're able to run a really wide rear wheel and you could easily have rear suspension with it as well. If you're going to stick with a hard tail and feel like fabricating, you could always make your own jack shaft. Whether or not you could incorporate the existing ATC axle would really be up to you as the fabricator.
I don't think I've ever seen anyone use a front hub for a rear. I suppose it's not impossible but my first thought is it doesn't sound like the best idea to me. I don't know everything though.
85 Tri-Zinger 60
85 ATC250SX
86 ATC250SX
87 ATC250SX
02 XR650L conversion
84 ATC 480R