There is allot of confusion surrounding 3705 carbs because they were made for MANY years after 64 production ended and sold over the counter. The most common thought is that production line versions were unstamped and only identified by the gold tags (stamped 3705S and having a ribbed tag design) however, some unstamped carbs were also sold over the counter, these would have similar gold tags but would be of various configuration depending on what vintage they were produced, some had the correct 3705S stampings on a ribbed tag but most wore later tags without the ribs stamped into them (like the examples shown above) and had "SA" after the 3705 rather than just "S". Then sometime after 64 production ended they started stamping the bases with 3705SA. The person who probably has the most experience with these carbs concerning these types of trivial details is Norm Brady, he has collected a (large) number of original 3705 carbs over the years and we've discussed it at length a few times, he knows his stuff! About the only consistancy with these carbs is that they are inconsistant!