Opening the engine is not worth the cost, unless you like paying a machine shop or un-needed work. The factory bottom end will support 400-500hp all day long if you wanted it too. It's the fuel and tuning that keep it alive. If the engine is healthy don't even touch the bottom end.
If you want 300hp, that is fairly easy on a blower. Swap in a mild camshaft, something like a XP cam, drop the pulley size down to a 3.0 or 3.2 size and do free flowing exhaust. Add some meth or run E85 fuel and get a good tune.
