Both motors can be built into strong performers, if you have the money and resources. The differences are the block, heads, intake, headers...everything they only share displacement. As far as which one is better, a 351W would be cheaper and a lot simpler to fit into a fox or SN95. The 351W can be done with pre made parts, the 351C would require alot of custom parts. You could make a 351W with 350-400 hp easy. A 351C on the other hand, depending if you went with 2 or 4 v heads would require reving the engine to 7000+ rpms to get any power. Building a 351C with 4v heads would be a waste in a daily driver, cause you'd have to rev it to the moon to make power, 351 ci is simply not enough to make use of the heads. If you really want to use a 351C, put the 2v Aussi heads on it with the wedge chambers. Any 351C stroker would be good, but would require alot of expensive custom parts. Another route would be to build a 347 stroker. it would be cheaper than any 351 swap.
The blocks are a bit different too... Windsor is a small block. The Cleveland is an intermediate block. Ain't quite a small block, but not quite (but sometimes listed as) a big block. When Ford designed the Cleveland (esp the 4bbl head version) they realized that you can make lotsa power if the heads breathe well. The 4bbl heads on a Cleveland were built to breathe.
The gas crunch and introduction of emissions laws killed development of the Cleveland. I think they were only made from like '71-'74. Then came the neutered 351M and 400M.
