I have:
1947-51 Chev Truck Shop Manual
1947-54 Chev Truck Factory Assembly Manual (probably the least useful, so far)
1960-69 Motor's Truck Repair Manual (for my '61 261). Bought it on Ebay.
Tom Brownell's "How to Restore your Chevrolet Pickup" which I heard might come out in a new edition.
"Chevrolet Pickup Red Book" by Motorbooks International. Covers '46-'72. Contains info on VIN's, specs, options, color codes, tranny and rear end codes but isn't complete in all respects. For instance, I think there is almost no reference to the 261!
Don't forget the Owners Manual. It contains lots of maintenance info and other interesting stuff.
1948 3/4-Ton 5-Window Flatbed Chevrolet 34 Years. Now with a '61 261, 848 head, Rochester Monojet carb, SM420 4-speed, 4.10 rear, dual reservoir MC, Bendix up front, 235/85R16 tires, 12-volt w/alternator, electric wipers and a modern radio in the glove box.