Well, since you already have a 283 in there, why not drive it. A lot of projects get off to big starts... I'm gonna change the engine, trans, rear, etc. And a couple years after they have been taken apart, you find them on craigslist, still in pieces.
Why not drive your truck the way it is and enjoy it, and do smaller projects to improve the drivabilty.
First thing to do is make sure the brakes are in good working order. If they aren't, that should be your first project. Power disc brake conversions that work with the straight axle start at about $700. Be honest with yourself in what your needs are. You can easily spend $500 to get the stock 4 wheel drums in working order, so spending a little bit more here might pay off.
Next, find the engine and transmission and rear end you want to use. You can use your truck to pick these items up and take them to a machine shop for rebuilding. So having your truck running is a plus. You might swap out the rear end one weekend, and then do the engine and transmission in another.
My point is don't tear the truck apart untill you are absolutely ready to, as they tend to sit and lose parts.
John
