you're missing doing it yourself, and learning what it costs to approach owning an old vehicle as a "collector" who wants something "cool" buying it "off the shelf" .... you can find good runners and used transmissions every day, find a setup you feel is decent and install it yourself instead of paying a specialty shop $100 an hour for the work plus their parts markup - settle for what'll make a good driveable rig and skip the spendy cool stuff, a '56 will wow anyone no matter how it sounds
Bill