According to some articles I've been reading they also made 351's but all the info is vague, some say the Nickel content is higher and walls are thicker as well as 4 bolt main that are stronger and thicker, Carrol Shelby also had to do a lot with this as he opened "Shelby de México" and promoted Racing heavily (articles:
ONE,
TWO,
THREE,
FOUR),
and lastly:
http://members.tripod.com/lyc_42/for...or/windsor.htm
sorry I could not be of more help!