Keep it as delivered from the factory/as original as possible...much cooler that way and nice find!
IMHO, the first order of business would be to keep meticulous records of the car. Start with looking for the build sheet (likely under the back seat, but may be pretty much anywhere depending on where the car came from). I would suspect it is still intact with how nice that car is. I would start a three ring binder with all the additional info about the car (try to contact previous owner(s), decode fender tag options, etc). You would be surprised how much info you can find out about your car from other members, the internet and the previous owner(s).
My anal retentive ways dictates that if I had a low mileage car such as this, I would buy a small notebook and document every tune-up, tank of gas, mileage and where I went with it to continue to trace the history of the car from the time I owned it forward.
Some people would say leave the engine bay alone, others would argue for you to detail it. Not sure which way people other members would regard that.
Like was echo'd by another member previously, you can find many solid 73 rust-free builders out there for a "fun" car, leave this one be. If you cant resist the urge to tinker, make sure the car is mechanically sound and clean up the engine bay. That car will run forever if maintained properly.
I know that I am curious about the story behind the car already.