Model A Ford's were built from 1928 to 1931 primarily with a single cylinder head design.
Pictured below is part number A-6050-A. This is the standard 4.22:1 compression ratio Model A engine cylinder head. This head uses 7/8-18 inch size spark plugs.
It has the four-stud water pump attachment design, and the separate water outlet on top of the head.
The original Model A cylinder head had no significant external markings. Later replacement heads made after 1931 frequently had the Ford script or Ford USA marked on top between the distributor hole and the head stud. Many also had casting dates and other assorted numbers, markings, and codes cast onto the surface.
Pictured above is a view of the standard Model A cylinder head with the 4.22:1 combustion chamber design.
Compare this pic to the 'Police' head and Model B head combustion chamber designs shown below.
Ford also produced an AF-6050 head for use with the small 3 inch bore Model A(F) engine sold in Great Britain.
In 1931, Ford introduced the A-6050-B high compression head (marked 'B'), often referred to as the 'Police' head. The compression ratio of the 'Police' head was 5.22:1, compared to the standard Model A head at 4.22:1.
Thanks to Craig Lewis of British Columbia, Canada for providing the great photos below of his original 'Police' head shown here on Ford Garage.
The 'Police' head has a large letter "B" (the part number suffix) cast in the top surface near the number two spark plug to easily identify it. The "B" does not signify a Model B head.
Pictured above is the combustion chamber of the A-6050-B 'Police' head.
This 'Police' head uses a different gasket than the standard Model A. Each gasket is designed to fit its respective combustion chamber.
The head gasket is designed based on the cylinder head, not the block. The gasket must fit the edge of the combustion chamber to seal properly and not expose the gasket to hot combustion gases. Using the wrong gaskets on heads can lead to early burn-out or blow-out of the gasket.
In 1932, Ford introduced the B-6050 cylinder head (marked 'C') pictured below. It is the standard 1932-34 Model B head having a 4.6:1 compression ratio.
The compression ratio is higher than that of a standard Model A cylinder head, yet it is less than the compression ratio of the Model A 'Police' head (marked 'B'). This Model B cylinder head also uses 7/8-18 inch size spark plugs.
As seen in the pic above, the Model B head had a large letter "C" cast in the top surface to aid dealer parts counter men in easily identifying it from other earlier heads. The "C" signifies a Model B head, not a so-called "Model C".
The Model B head is identified by the three-bolt water pump attachment. The three-bolt water pump has an integral water outlet as part of the pump casting. There is no separate water outlet mounted to the head.
Pictured above is a view of the standard Model B cylinder head having the 4.6:1 ratio combustion chamber design. This is the so-called heart-shaped combustion chamber.
Also seen on the Model B head above are the two "steam holes" on either side of the center head stud. These holes are quite near the edge of the Model B gasket and are often difficult to seal against water.
Using a Model A head gasket with a Model B head or block is not advised since the gasket profile is different and is even closer to the edge of the steam holes in the head (and block).
The B-6050 is the only cylinder head originally used on the US-marketed 1932-34 four cylinder engines.
Ford also produced a BF-6050 head for use with the small 3 inch bore Model B(F) engine produced in Great Britain in the early and mid 1930's. The BF prefix head has a different stud spacing pattern, and will not fit on a Model A, AF, or B block. It will only fit a BF block.
In later years Ford-Köln in Germany produced a 7.0:1 higher compression ratio version head BG-6050-B which used 18mm spark plugs, as well as an 8.5:1 head numbered G28TG-6050 which was used for wood gas compressor use.
There is also a Ford-Köln Model B head marked G38T-6050 which has a combustion chamber very close to a Model A 'Police' head, but with the three bolt water pump provision and metric spark plugs. It's compression ratio was likely in the 5-6:1 range.
In addition, GAZ produced the M-6050 Model B style 4.6:1 ratio combustion chamber cylinder head in the Soviet Union from the 1930's to 1950's. See related link below.