It would be way cheaper to buy a truck that already has a V8 in it. But.... if it was mine, and I had the time, I'd build a SB 427ci V8 Ford engine and install it. It will take some mods to do this upgrade, including new rear-end, new transmission, new custom drive line, engine compartment mods and possible new or custom cross member.
Here's a short block: http://www.competitionproducts.com/prodinfo.asp?number=427FFT
You can build this cheaper than buying this kit by buying just the "stroker kit" and having your own block machined.