Just some friendly advice here. Unless you're very mechanically confident with these engines, I would steer away from tearing into the bottom end. It's extremely difficult to build one back up without spinning a bearing. The bolts are all TTY, and you have to be very exact with your tightening.
Now, that said....if you want to swap out a SC engine, that would be the easiest. If you still want to top swap an engine, and plan on getting a NA engine to do it, get one from the newer GP's, they have the stronger powdered metal rods that will hold up a little better to the abuse. It's a fine line to walk on a NA engine, but you can make good power with them with a larger pulley. It takes much more horsepower to run a 3.0 than it does a 3.8.
Just my 2 cents.
