Like the title says; how feasible is it to convert an oldie on what I believe is the GMC/Chevy Viking platform, to 4x4? This was essentially their medium duty truck chassis, I believe. This isn't a photo of the exact bus I'm looking at, but it's the right platform, right year (the one I'm considering is a 4 window, about 22 ft):
I currently have a completely different, modern bus in mind, but provided I don't win that auction, I'm considering taking my future skoolie build in a completely different direction; restoring a small, old bus. At the very least I intend to repower with a modern and more fuel efficient engine like the 5.9. Given I get a lot of snow, I'd also like to add a selectable locker. For this, I'm thinking of changing the rear out for a Dana S130 since they're relatively cheap and easy to come by for a 14,000lb+ axle. I could also keep the stock axle, provided I can change the ratio to match a Dana 60 front if I do go 4x4. The bus I'm considering has a 2 speed rear, possibly a Spicer. I'm not sure if I could make that work if I kept it and added a Dana 60 front?
What kind of work/how much work would I be getting into? Anything fundamentally different from swapping axles on any other truck? The one thing that has me worried is spring center-to-center distances on a 1959 GMC versus whatever axles I'd be getting... but I assume there'd be no issue in repositioning spring seats on the axle? Likewise I assume it'd be best to find an engine + transmission with a T-case, or would it be more cost effective to just buy an entire "rolling chassis" from, say, a Dodge 3500 or up?

I currently have a completely different, modern bus in mind, but provided I don't win that auction, I'm considering taking my future skoolie build in a completely different direction; restoring a small, old bus. At the very least I intend to repower with a modern and more fuel efficient engine like the 5.9. Given I get a lot of snow, I'd also like to add a selectable locker. For this, I'm thinking of changing the rear out for a Dana S130 since they're relatively cheap and easy to come by for a 14,000lb+ axle. I could also keep the stock axle, provided I can change the ratio to match a Dana 60 front if I do go 4x4. The bus I'm considering has a 2 speed rear, possibly a Spicer. I'm not sure if I could make that work if I kept it and added a Dana 60 front?
What kind of work/how much work would I be getting into? Anything fundamentally different from swapping axles on any other truck? The one thing that has me worried is spring center-to-center distances on a 1959 GMC versus whatever axles I'd be getting... but I assume there'd be no issue in repositioning spring seats on the axle? Likewise I assume it'd be best to find an engine + transmission with a T-case, or would it be more cost effective to just buy an entire "rolling chassis" from, say, a Dodge 3500 or up?