Pete: Where is that number located on the block? Is it stamped or cast into the block?
The above answers are totally correct. But, you could still have an earlier cast block installed in a later year car. The Merc block below appears to be a 1949 but, it has 1951 Merc narrow belt water pumps. 1949-50 Mercs had wide belts installed differently than 51-53 Fords and mercs..
There are no differences between the Merc and Ford blocks other than
the color they were painted. Even then, it could be a repaint.
Having the components that were bolted onto the block might tell you a bit more. For instance, the 49-53 Merc intakes and carbs were 4 bolt "teapot" style. Merc. oil pans were (rear sump) also different than Ford cars. Do you have the oil pan?
Plus, the 1951 Mercs had a cast iron oil pump idler gear cover. Fords had stamped steel.