Recently acquired what I thought was a matched set of 1967 435 hp carbs. The ends are 3659s date code 691. The center carb is what I'm questioning. It is a 3660 but has two date codes. The first appears to be 864 but it is partially overlaid by a second date code of 692. I don't know what I've got here. Can anyone help me out on decoding the date codes? Thanks