I know that this is a bit of a stale post but wanted to add that the color of the top stamp changed over 64 to 66. The bottom left is a 3L dated original, bottom center is a 6B dated original. Note how the earlier one the color is more towards Ford blue, while the 66 is more of a teal or aqua. The others are pics of the the two repro lids from AMK posted earlier in the thread and one of the complete repro regulators that AMK used to sell, all having an aqua color. Also note how the stamp on the repros is much thicker, almost looks silk screened, rather than ink stamped as the originals were.
-Scott