If you're looking for hp in the 300's, go with the 4200. It made 290 stock, you won't need to do anything but free up the intake and exhaust. My only beef with these engines is they're kind of ugly as it's hard to hide all the electronics.
If you spend the time&money to get the 4200 running now, you'll be able to upgrade a lot more later. I think this is the better investment in the long run.
