Just purchased a 1975 Firebird Formula. Need advice on updating the factory exhaust.?

My uncle puchased the car new in 1975. It's been garage kept since 1976. I recently purchased it from his son. The car is in very nice shape and ALL original (except it's missing the 8 track and has a new cam and lifters). I want to make it purr, but am afraid to change anything since it's unique to have a car that has not been modified. Any thoughts?