if looking at a task force. check closely for the usual rusted spots. water comes in the cowl grille ahead of the windshield, drains down the inner cowls behind the fenders and out the bottom. problem is the drain at the bottom is pretty small and gets clogged. that causes a back up and standing water in the inner cowls and if enough water is trapped it drains out into the cab and out onto the floor through the side vents. a lot of these cabs have this problem which ends up rusting out the floor, hinge pillars, steps, rockers, front cab mounts and lower fender mounts. these would be good spots to check closely from underneath. the area above the windshield is also known to get pin holes as well as the rest of the area just above the rain drip rail. the perimeter of the rear cab window is also prone to the same pinholes depending on where the truck was stored etc. obviously the rear cab corners are prone to rust but sometimes the larger trucks, especially ones that are used mostly in the summer/fall for farm duties or come from desert areas, are good candidates. a lot of guys use the larger truck donors for their cabs on 1/2 tons, using their small truck sheet metal for the rest. the front sheet metal on the big trucks is actually wider/longer and the wheel openings are bigger. this could be an advantage if building a bigger truck with a donor frame or upgraded IFS/solid axle suspension on the original frame.
I would have to agree on the use of the old style split rims. they are not worth the hazard.
if a bigger truck, with duallies, is what you want then a larger truck donor may fit your plans with a frame swap to a newer chassis with better brakes, better steering, normal wheels and tire sizes, better gear ratios, easier to find parts etc. or, since these frames are basically flat, you could install the front suspension and steering from a newer truck under the old truck frame, swap out the rear axle for the newer style and gear ratio, brakes etc. shorten the frame to your desired length and, BOOM, done. well besides a steering column, power brake and master cylinder mount, wiring, etc. there are those on this site who build their own frames using the dimensions needed/gleaned from the assembly manual blueprints.
here is a link for the factory assembly manual and also the old car manuals project. maybe help you see the differences in frames, body dimensions etc.
http://www.trifive.com/55-59Assy.pdf
http://chevy.oldcarmanualproject.com...esto/56134.htm