You tell me Bill. Don asked same question Sept 6. I replied "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."
As you say the hood louvers space is another but that carries on with the 40. If vehicle has its orig W5A the serial range helps to identify if M2 or M4 to a point. Don's car has an M2 engine.
Its like the 1932 614 versus the 31 614 upgrades. All I can see is twin bar bumpers 1931 and single bar 32. Inside / outside door handles 1931 spear, 1932 now 1930 Essex and outside ones ?? Tires 1931 4:75 / 5:00 x 19 1931 and 1932 5:25 / 5:50 x 19. Tire Co confirmed the larger size only 32 as they have the old books. 1932 could have W8A carb or J4A (mine)
Think Gord said only difference between the E-618 and E-670 Fronty was the rad crest was moved down the grill. There's another thing no where does it say 618 / 670, the vin plate model is E for both. vin wise E xxxx is 1931 and G xxxx is 32.
Where Are You From? Ottawa Ontario Canada
Do You own a car built by Durant? 1932 614 sedan made by Dominion Motors