See
http://www.hipomustang.com/hpmx/topic.asp?TOPIC_ID=795
SM2S is a '66 Shelby Cobra part.
Holley carbs have a number on the front air horn flange. It tells you the model number on the first line and the rebuild kit part number on the second line. Example:
0-6262 <- carb model
37-605 <- kit to use when rebuilding carb.
See
http://www.holley.com/HiOctn/ProdLine/CarbList.pdf
for a listing of Holley carbs.