I am interested in what others have to say about this issue as well, I have swapped the frame on my 1 ton witha 78 chevy 1ton frame. The biggest issue that is I had was the radiator fitting with the cbb and the wheel spacing. I think that I have the radiator issue resolved and the wheel spacing under the front fenders really isn't a problem. I am thinking of some ideas that might resolve that but I need to do some measureing on a mid 70's 3/4 ton to make sure it will work. My idea, just to put it out there, is using 3/4 ton front hubs and have a spacer machined to provide adequate back spacing to allow a full turning radius and keep the wheels inside the fender wells.
I have some pics and write up on my truck below(see signature). Follow this
http://community.webshots.com/slideshow/568633139UrmOzO?mediaPosition=1 to see the wheel spacing deminsion of my truck. I have measured a 1 1/2 or 2 ton truck and the fenders are bigger but not much if any wider maybe 1/4" too close to determine. My write up states why I chose this route. I have read several different gallery write ups that utilize different methods to upgrade thier truck with suspension,steering and gear ratios that seem to be easier than a frame swap. See this
http://www.stovebolt.com/gallery/turner_ricky_1945.html The biggest thing is like Grigg said how will you use the truck? The anwer will give you a better determination of how you need to build your truck. Good luck and do
lots of research.