How is the engine itself?? Before you buy a lot of parts, you might want to do a leak down check and make sure the rings and valves are still up to the task. If the engine is sound and you buy matched components, (Edelbrock RPM package, or the like) the changes you mentioned should get you around 30 to 45 horse. Hard to say. Make sure you have ignition that can handle the other improvements, too. Oh, if you can find a set, the old Tri Y headers really worked good on the 289's.