A new long block is going to set you back a pretty penny, and isn't needed if your current engine is in good running order. I understand the reasoning behind buying a new engine for the peace of mind, but it isn't worth it if your current engine is still in good working order. A compression/valve adjustment/recheck comp and you will have a good idea of the condition of the engine.

You should be able to buy a used block and do a power build for less than a new engine will cost you. If you buy a new engine and then do a build-up of the old one, you are spending the twice the money, money that you wont recoup when you go to sell the new(by then used engine), money that could be better spent on upgrades to your truck like gears and tires, bumpers, winch, etc.

I am not trying to talk you out of buying a new engine, it just doesn't seem like you need one at the moment. Contact enginebuilders and see what a head(w/oversized valves) and the rest of the engine parts will run(for bored cyls, and a full rebuild). I am figuring about $1k plus shop work for enlarging the cyls(should be under $300), and if your crank needs work figure about $250 more. At $1550, your still under the cost of new engine and about the price of a used one from most of the engine suppliers.