IMHO, go to a JY and pick up a late 60s, early 70s truck engine. They're cheap and the blocks are stong (4 bolt mains etc). Find one that has the block number that ends with xxxxxx10. If you plan to build your own, this is a good starting point. If the bottom end is in good shape, pick up a cam, lifters, set of vortec heads and inlet manifold and carb. $2000 plus the price of the block and you will have a decent (300hp or so) motor.
Tim