318,340 or 360?
If you have a limited budget, find a running (like so you can hear it) 360 engine. Pay more for the engine, and do less to it. Say, a 4bbl intake and carb, plus some cheapie headers, and drop it in. Some of my most fun cars had medium milage good running stock engines in them at first. Bolt ons can carry you a long way later or as money develops. A stock 360, a decent rear, and 3.55s or 3.91s and you'll be hard pressed to keep tires on it. (dont tell Dad...and dont forget to remove the rubber from the wheel wells...It was a dead give-a-way to my father...lol)