[Jack21]

You should be able to find the block ID on the passengers side of the block, under the starter.

A 351W, looks like a tall 302. The timing cover is cast pot metal or aluminum, and is bolted to the front of the engine. The heads sit about an inch above the water pump inlet (wheras the 302 heads sit even with the water pump inlet).

A 351M looks like a tall Cleveland. (To me it even looks more like an Oldsmobile motor) The timing cover is part of the block casting, and is covered with a stamped steel plate. And there is little aftermarket parts for the "M".