Yo,the 351M/400 blocks were cast at either the Cleveland Foundry, or at the Michigan Casting Center only. The Michigans will have a "MCC" stamped near the oil pressure sender port. Cleveland Foundry will be stamped "CF" in the same location.
from Ford @ http://www.oemfordparts.com/faq/smallblockv8.htm
289/302/351W engines is a front cover and water exits the intake manifold face of the cylinder head through the intake manifold to the radiator. 351C/351M/400 engines do not use a front cover. The block is extended and covered with a flat stamping. Water exits the combustion face of the head and into the block, and then to the radiator. Windsor and Cleveland head physically interchange, but some modification is required to accommodate the differences in water passages.
The Windsor engine plant builds this engine; hence the name. Normally, this isnít important. But another engine, the 351C (for Cleveland engine plant), has the same displacement. Thatís about all they have in common. So, itís always important to differentiate between the two. The 351W is a beefier block than the 289/302, but has the same bore spacing (4.38") and bore diameter (4.00"), so heads retrofit. A higher deck height requires a unique intake manifold. Main journals (3.00"0 are larger than the 289/302 (2.25"). Camshafts interchange, but the 351W has a different firing order: (1-3-7-2-6-5-4-8) vs. (1-5-4-2-6-3-7-8) for the 289/302, except the 1982 and later 302 HO which use the 351W firing order.
The 351W351M (MOUNTED) AND 400
The 351M and 400 are similar in design to the 351C, but there are subtle differences. Both the 351M and 400 blocks are 1.100" taller and have larger main journal diameters. Engine mounts are unique. Bell housing pattern is the 429/460 design.
has been used from 1969 to the current year.