Service bed dually?
Wouldn't that be a C&C?
If so, the rear spring perches will be too close together for your pickup frame

Dual calipers are all the same, rear shoes could be different widths.
(12 x 3 or 2 1/2")
10.25" full floaters are much easier to deal with, as the drums slide right off.

350's just have higher lift blocks in the rear, Plus springs, depending on GVW...
But their solid front axle is much easier to lift without all the alignment issues involved with the TTB front end.

Personally, if you are swapping engines, transmission and both axles I think it would be easier to just swap your body onto a solid 350 chassis.
You could then take the time to clean up the frame, do the lift, whatever.
The VIN comes with your cab, so there should be no title issues.