[Zedder]

From the WLA website:

WLAs did not receive a frame tag or frame number and were identified by the engine number, embossed on the left side of the crankcase in the following fashion '42WLAXXXXX'. This was the Vehicle Identification Number (VIN).
Furthermore all Harley-Davidson engine crankcases were numbered during their production on the lower front side of both halves by the year of manufacture followed by the sequence in which the crankcases were mated together (ie 42-12345 = the 12345th engine assembled in 1942).
This being said, there's no proof that all 42WLA motors were actually made in succession. So when Motor 42WLA26890 has Crankcase Numbers 42-28352 ; this does not necessarily mean that Engine 42WLA26891 will have Crankcase Numbers 42-28353.......

45 ci Flathead Engines were also used in Canadian WLCs and Servicars and motors for other models were made during the same timeframe...... Although of course, you shouldn't find a 1944 Crankcase Number on a Type II WLA........

So to accurately date a 42WLA, you need to look at the 42WLAXXXXX engine number and start from there. Only the Types VI and VII had the later style data plate which lists the engine serial number.