Don the engine serial number is not on the head. Heads, blocks are cast long before the get used so this W5A could have been used M2, M4, 40. As example the 1930 614 came out Jan 4 1930 and used the 22A engine. Heads, blocks have casting dates Oct 1929 up into 1931. There are no 22A's recorded with dates after 1931, which is probably why they came out with the 32A in 1932, but casting dates on those are a mystery with the alpha, numeric, alpha. So far no one has been able to crack that meaning in other clubs with vehicles using Continental engines.
Serial plate is on the block, drivers side below the manifold and will start most likely 54xxxx or 55xxxx for M4
Are there not other differences between M2 ad M4 to update the need to call them M4 ? As Terry's site says "new type body hardware" M2 seems to have two medallions on the front bumper and M4 a single center one, as an example.
Where Are You From? Ottawa Ontario Canada
Do You own a car built by Durant? 1932 614 sedan made by Dominion Motors