1 ton axle swap questions

[HvyChevy]

My 1970 is finally going to get paint on it, so I'm getting my parts together so I can get to work on it when it gets home.

I have a Dana 60 and a 14BFF out of a 1986 Chevy 1 ton, flat bed, single wheel truck. The Dana 60 measures 32" from spring perch to spring perch. The 14BFF measures 40" from perch to perch.

The 14BFF is 54" from backing plate to backing plate. Is a disc brake kit going to go on this, and is it too narrow?

Anything I need to know, or get, to make these axles go in?

Thanks for any input,
Dan