Just a quick note to add to all the excellent advice. What are you looking for? If you want a bike that is "whippier" accelerates faster and feels more sprightly its mostly wheels. Get a great set of rims on great hubs with double butted spokes and the feel of the bike will come alive. Match that with lightweight tubes and good tires and you can seriously reduce your rotational mass and feel a real difference. Quicker acceleration, springier lively feel. Its all wheels. Look at 80's Campy nuovo record or mavic for hubs both are excellent and keep the vintage vibe. Without losing the vintage look try a carbon seatpost, newer alloy cranks (make sure you get ones that have a bcd thats still in use or available, modern brakes and levers. Bottom brackets do weigh a ton.
good luck