Dana 60? In an '88 'Burban? I think that it may actually be a 14 bolt GM corporate full floater.
I don't think that GM used Dana axles in their trucks in the '80s for the rear. Either way, it'll be plenty stout. I beleive that the only difference for a dually rear on a GM is wheel stud lenght, I've never seen any type of adapter on dual wheel American trucks, regardless of brand. The last dually I saw with an adapter was a Toyota, and it was an aftermarket conversion. Some sort of motor home thing, I remember the owner wanting the cheapest tires for it.
