[dsraven]

are you planning a 4x4 dually or single rear wheel?
there are a few ways to get to the 4x4 version, some include a frame swap to a newer chassis that is already a 4x4. it can be some work and may put the truck out of commission for a long time. it depends on your drive to get it done, personal life committments, a place to do the work and store lots of big parts, your skill level and tools available. oh yeah, then there is the budget. I always recommend talking with someone who is knowledgeable about doing this sort of thing. prefferably someone who has actually done it. ask about what it takes, budget wise and parts wise before you commit to tearing down your truck. download a copy of the factory assembly manual (trifive site has it. 55-59 chevrolet truck factory assembly manual). do some plans and drawings on paper with actual dimensions etc. do all that waaaay before you start chopping things up, thats how these things get to be a project for sale or a bunch of parts taking up space where you should be parking.
your truck looks to be amazing shape. great find.