They are both Ford smallblocks. The main difference is up top. A windsor is a wedge style head with all the valves in a straight line, and the cleveland uses a canted valve head (intake and exhaust valves are at different angles in reference to the bore). Coolant routing through the heads is a little different.

Bore centerlines are the same, same number of head bolts, on one the water pump spacer is integral to the block, on the other the water pump spacer is a seperate casting.