I am not 100% sure but I am betting the stepside will bolt right on. GM wouldn't change the frame for each bed design. I would bet you could bolt a real late model bed right on the frame if you can't find a old one.
As for the work, its normal for there to be six hold down bolts, a ground wire, and posible fuel filler neck. Once unbolted, use three or four guys or a engine hoist to pick it up. You are looking at less then 300 pounds. If you had the new bed, you could do it in a afternoon. Joe
