Will you be keeping the boat in the water or on a trailer? Most people who race (newer) Lightnings drysail them and have no bottom paint on the hull and stainless steel centerboards.
If you are going to paint your bronze board in order to prevent fouling (if you're keeping the boat in the water) you probably don't need to paint the whole thing... just the portion that will remain submerged in the centerboard box at the mooring. Contact a reputable marine paint manufacturer (Interlux, Pettit) for advice on prepping, priming and painting bronze. Good luck and be careful about running hard aground. Bronze can bend and twist more easily than steel and I've seen it happen with bronze centerboards!
“So we beat on, boats against the current, borne back ceaselessly into the past.”