International 4700 Low-Pro Suspension - frame stretch and mods

I have purchased an early 2000's Int 4700 that started life as ambulance but was turned into a 12 ft flatbed. It has the DT 466, 5 speed Allison automatic, Spicer rear end, hydraulic brakes with air emergency/park.

I'm getting ready to have the frame stretched a bit to accommodate a slightly longer 14 ft+ bed and a heavy rear pintle hitch plate. I am wondering if there is any way I can turn this into a tandem 4x6 while keeping the low-pro suspension, and if I will have to lose the air suspension on the rear to do it. Is it a simple axle or hub swap from 10 to the smaller 8 lug hubs? Should I just find a complete tandem rear half from the junkyard and have that welded on instead when I do the stretch?

I am in the telecom construction biz and this it going to be pulling things like smallish directional drill or an excavator on bumper-pull trailers. The bed will have a water tank(s) and mixing system plus tools etc. I do plan on changing out the instrument cluster and adding everything needed to be able to pull an air brake trailer behind it sometimes.

Thanks for any input.

Also, as this isn't specifically/entirely engine related, if you know of another forum(s) that these questions would be better posed in, please point me towards it.