Before you spend any money, I think you need to be honest with yourself about the condition of the rest of the truck, and what else you want to do. What condition is the interior in? Does the hood close all the way, or is there damage there. How many miles? How well does it shift? How does it run? Are you going to be spending money on fuel pumps, alternators, batteries, etc. If the bed rusted that bad from acid, you need to look carefully at the frame underneath, along with the brake lines, fuel lines, and suspension parts. Are you willing to spend another $1000 rebuilding the motor? Are you willing to spend another $1000 on the transmission? Are you thinking about a paint job for the truck to stop any further decay?
Since this was your dads truck, and judging by your list of vehicles it seems your in a place where you can spend some money on vehicles, I think I would go the aluminum flat bed route. Best case, you put some cool wheels on this, new tires, new gas tank, carb rebuild, new plugs and wires, new battery, clean it up a bit, remove the tool box, and make it reliable. You should be able to find a new chrome rear bumper for cheap. Worst case, you can always put the flatbed on your next truck or sell it for much of the money you have in it.
A second stock bed will already have a lot of years on it, and will decay like the original if not rhino-lined. Once it decays, it loses all value, and once rhino-lined, it loses all value, so either way its kind of throwing money away.
I would take your 16.5" wheels off, and replace with 16" or 17". Tires will be cheaper and much better quality. You will be able to find tires without special ordering. Do not try to put 16s on 16.5" wheels. Some shady places will try and do that, but it is dangerous. If you already have 16" wheels, you may be able to find a place that will blast and powder coat them for cheap. Some places do this on large numbers of semi truck wheels for cheap.
