Mike, if your looking for a big power jump I would build a different Cleveland to your liking while still enjoying your car as is. I would ensure your new Cleveland while being built follows George's recommendations and that the proper thermostat, a recommended water pump and the oversized pulley that many run on here are used. Doing this may help completely avoiding changing out a rad and fans later. While disassembling your car for the swap I would photograph and bag and tag everything. This will keep things documented and easier to return to stock If ever desired with your factory motor on a stand.
If a smaller jump in power is sufficient I would remove the smog, try a different intake and tuned carb or fuel injection and check out some exhaust options. Headers maybe from Pat Mical, or mufflers and tips from Dennis Quella. Then get the car tuned on a chassis dyno. That can all be done without opening up the motor. Meeting the smog requirements back then may have killed a lot of hp.
If that doesn't satisfy your power need, then you know you need to do another motor or dig deeper into the factory one. Regardless on a car like that, bag and tag everything.
Lucky guy having a car like that.