I would determine what your goals/funds are and then do in stages. If you are not going to compete in shows or not worried about resale value and want more power then a swap might be better/cheaper. Go look at the price of overhaul kits for the present engine vs a 60-70s engine. If you keep the present engine, would overhaul first, drive around and get the feel of it, if you get bored after a while then add dual headers and multi carbs, high energy ignition. If you get bored with that and have the funds then add a turbo, but don't expect the overhaul to last very long. Lower end crankshaft/mains strength and old piston designs probably aren't suited for a turbo. Do things in stages to have something to compare against.