Dang. Learn something new every day!
http://www.ipdb.org/search.pl?mfgid=413&yr=1964&sortby=name&searchtype=advanced
shows all 1964 Williams except Zig-Zag and Wing Ding have red flippers. Never knew that.
Now....what to do? Sand and paint red, put up a "parts wanted" ad, search ebay. Swap out for another style, sand and powdercoat. My guess is that these were powdercoated, and that is why they are so resistant to chemicals. Just a crappy guess though.