What all is involved in cab swap

[JON70CST]

Hey guys,
I am restoring a 68 lwb fleet side, but my current box is too far gone to be repaired i believe. The previous owner tried, but failed miserabley. I am currently on the prowl for a relatively rust free or at least repairable replacement cab (not having very much success, so any suggestions on where to find one would be great as well), but my biggest question is what happens when i do find one with the VIN and tags, title, etc. Might be a stupid question , but i'm still relatively new at this. THANK GOD FOR THIS SITE THOUGH! , so many great ideas, suggestions, and members!