351W and 351C are completly different engines with no major parts interchangability.

The 351W was basically a larger version of the 289/302 SB Ford engine, with a taller deck to acomidate the 1/2" longer stroke.

The 351C uses a completly different block/head configuration which is a bit wider than the 351W, making it a bit more dificult to fit into tight engine compartments.

The 351C had bigger valve better flowing heads than the Winsor.

Many people feel that the Windsor has a better oiling system and stronger bottom end than the C.levland.

One popular swap several years ago was the addition of 351C 2BBL heads onto Windsor blocks (refered to as a Clevor), but as I recall, this took special head gaskgets and a special manifold to make it work.