A message for Jim Benjaminson, or whomever can assist. On Sept 27, 2023 I submitted a question about a 37 Ply slantback that I had just purchased. Jim sent info dated Sept 28, 2008 stating # of vehicles built, registered vehicles,P3/P4 series, etc. My ser # is 1213305 body style 911-10992. Is it a P3 or P4? Was it one of 7,926 built, or one of ???? It has a back "hatch" but it is not a humpback style. I checked www.ply33.com/models/p4/#production, and i'm still confused. also I have only seen 3 others like mine. PLEASE HELP. Thank you, KennyG
Your serial number indicates it is a P3. On my same website that you link to there is a serial number look up tool at https://www.ply33.com/Misc/vin which returns this information in the "1924 through 1974 Mopar Number Decode" tool located on the upper right:
Serial Number 1213305
Found in range 1184001 to 1237460
Serial 29305 of 53460
Year 1937
Make Plymouth
Model Name Business
Model Code P3
Plant Detroit
Engine 6 cylinder 201.3 cu.in. L-head
Wheelbase 112 inches
Back in that era Plymouth did not call any of their body styles a "slantback". That is a modern term. The "touring sedan" (two door or four door) had a built in trunk which I am guessing you are calling a "humpback style". The regular plain old "sedan" did not have that style trunk. I am not sure for 1937, but the earlier plain sedans had no trunk at all unless you purchased the bolt on accessory trunk.
A photo of your car might help us tell you if it was a sedan or a touring sedan.
Photos will really help to solve your problem. So always have a pic of what you are asking about and maybe you will get some answers.