Well, I guess I'll be the one dissenter, I gotta go against the flow here, I say longbed!!!
If I were building another rig, I would get a M1008 'cause it's already got the good stuff: th400, Dana 60 4.56, 14BFF 4.56 Detroit! The only weak points are 6.2 and 208. I'd put in a Banks kit and a 203/205 doubler, problem solved! I'd bob about a foot off the rear overhang, add 4" lift, crossover, a front locker, 38" Michelins on some 16" van wheels, boom, instant fun machine!
Or, start with a civvie one ton (this'd be harder to find but, I saw one for sale I almost bought (don't need another project). Find a 1-ton dually single cab, 454, th400, 205, Dana 60, 14BFF. Add a doubler, F/R lockers, 4.56 gears, standard H1 12 bolts w/ PVC (Stazworks or USA 6X6) inserts, 37" MT's (cheap good tire), 4" lift, crossover, take off the dually fenders and bob a foot off the bed, add fuel injection, SWEET!
Seems to me it's cheaper to start with a one ton and bob the bed than to start with a 1/2 ton shortbed and swap all the one ton stuff in.
