In the ’55 Ford parts catalog, a three sheave pulley is listed for the passenger cars with the 60 amp generator and/or air conditioning. My own ’55 wagon has an integral 3 sheave damper pulley on it and that car is factory equipped with a 60 amp generator, air conditioning, and power steering. Looking at the ’57 parts catalog, the same style three sheave pulley was also used on the ’57 Ford passenger cars with the 30 & 50 amp generators and with the 50 & 100 amp alternators. For the Mercs, I recently pulled apart an original ’57 Merc 312 that had a 3 sheave pulley on it also.
Here’s the thread that also includes some pictures.
http://www.y-blocksforever.com/forums/Topic50937-3-1.aspx