Not necessarily. If the original trans is being used, the rear U joint can be adapted to whatever yoke is on the replacement rearend using a dual size u joint. Did just that once on a '49 3800 that we had swapped a Dana 60 out of a 3/4 ton Dodge van into. The Van yoke took a smaller cap size, so we installed a Spicer u joint with dual cap sizes. Worked just fine.
Now, without being 100% sure of what direction fiveoh is going, it's hard to say what diff should be used or what to do with the driveshaft. I will say that you're going to looking at a front axle swap, too, as none of the aftermarket 5 lug parts will fit the 1 ton axle.
