47-55.1 No ribs on my firewall?

[Northern 52]

I am currently working on a potential firewall brake installation option on my 1952. Upon doing some research (the good old internet) I notice that my firewall that is stock 1952, has no ribs. I believe they are just strengthening ribs on both the driver and passenger sides above the foot wells. I don't think it will have any negative affects but am just curious as to why they are not there.

Was it a particular year or production batch? Does anyone know why this might be?

By the way, my Canadian 52 has features of an earlier model (cab side vents and no door vent windows) but is tagged with what looks like an original 1952 serial number plate in the door jamb.