what do you want to end up with in the end? a old style commercial truck on a new chassis? that is, a 1 ton cab and chassis with a deck or commercial box? do you want a conventional truck with a regular truck box behind it? a long (like 9 ft) box like some old 1 tons had?
if you plan on a commercial box behind the cab there are options available at truck outfitters for an "army" look box.very practical but not that appealing to the eye of most custom guys. google rebco for their version. check out the coe collection here for some ideas of what guys have done for something behind their cab
http://67-72chevytrucks.com/vboard/s...d.php?t=162216
if you plan on having a pick up box behind the cab, not a deck, then plan on a short sided bed, inside, because the newer style trucks have a kick up behind the cab so either the cab has to raise up to match the box height or the box has to be "cut down" inside to match the lower cab height. if you plan on having a deck, like a farm truck or a car hauler, then it wouldn't matter so much.
you may have to cut the frame and shorten it if you plan on a normal truck box, unless you fab up something to your likingback there and attach some truck style fenders to it. that would mean a driveshaft refit as well. also check the frame width and compare to a box to see if a regular truck box will fit on the (I assume) wider frame of the newer style trucks. the old truck has a tapered frame that was narrower in the front. if memory serves me. there is also the 9ft box option.
check the front wheel centerline dimension from the firewall on the old truck and compare to see roughly where the cab will need to sit in comparison to the engine on the newer style frame. the hood and fenders on the 1.5-2 ton trucks were a bit longer I think so you may have some extra clearance there for a rad and fan, if the cab has to sit too far forward.
anyway, just some thoughts. post up a few pics of what you have to work with and you may get more results