Identify a 351-C Engine
Use the table below to see some of the obvious, easily visible characteristics that allow diferentition between the 335 family (Cleveland, 351, 400 and 351/400M) and the 90°V family (Windsors - 289, 302 351W).
 

Cleveland versus Windsor Families

Rocker Covers    Clevelands: Large covers with 2 different angles on the top and 8 hold-down bolts.                   Windsors:   Smaller covers, flat topped with 6 hold-down bolts.
Water Inlet (Intakes) Clevelands:  Water inlet is in the top of the block. Windsors:    Water inlet is in the intake manifold. Want to see lots more intakes? Click here! Distributor Angle Clevelands: Distributor is tilted slightly towards the passenger side. Windsors:   Distributor is verticle The top picture to the right shows the 351-C tilted distributor (on my very dirty engine) and to its left, the water passage going down into the engine.         In the lower picture, a 351-W, you can see the vertical distributor and the horizontal water inlet that goes into the intake manifold. (351-W photo courtesy of Indy Mustang.)
Head Markings Clevelands have a raise letter/number in the upper left corner of the head, which is visible with the rocker cover in place. The 2V's have a number "2"; the 4V's have the number "4"; and the 351/400M's have a letter "M".       The picture to the right is my 2V head.
Spark Plugs Cleveland: Small diameter, 14mm spark plugs. Windsor:  Standard spark plugs with a 5/8" thread (15/16" inch wrench).

To distinguish between a 351-C from a 400-C, double check the year of manufacture and look at the label attached to the rocker cover. To distinguish the 351 from the 351/400M, look at the year of production, the label on the rocker cover and look for the  "M" on the head, as shown above.