Ditto with FastFord - 351-C is a small block bellhousing. They actually came with FMX's on some of those 'Stangs. Don't tell anyone, but even though 351-M/400 have big block bellhousings, they are still considered "small block" engines. SSSHHHHH!
(HEY FASTFORD...YOU GOT A 351-C, too!!! Very nice)