Most likely its a Windsor. They stopped making 351Cs in 1974.
Easiest way to tell is the top radiator hose attaches horizontally to the W intake.
The top radiator hose attaches verticaly directly to the block.
it is not the origanal motor for the truck. it dos have the vertical radiator hose into the block. places on the web also said the valve covers will have 8 bolts for the clevland and 6 for the windsor.