Mather produced boxcars with a few different interior heights. There were also some 36-foot Mather boxcars rolling around before 1930. Just because it is labeled as a Mather boxcar, stock car, or reefer does not mean they are all the same. They came from the same builder. IIRC, at one point the AC&Y had two series of Mather boxcars with different interior heights.
I suspect the Proto2000 models produced by Life-Like followed prototypes for certain time frames. Mather leased these cars and they were reused after leases expired. The cars returned to the Mather shops for repaint and reletter for the new lessee. You will need to consult the ORER for your modeling period to determine where the Mather cars were used.
From: main@RealSTMFC.groups.io <main@RealSTMFC.groups.io> On Behalf Of mopacfirst
Sent: Tuesday, April 30, 2019 8:00 AM
Subject: Re: [RealSTMFC] Manufacturers Railway Mather box
I can see an issue on the height, because from looking at the pictures of car bodies from the Proto kits on eBay, they all look the same even though there were some that were quite a bit taller. I found another good source in an ad for RY models in O scale, and there the cars are separated by height. The one I'm thinking of is 7'-8" IH, which seemed to be a common height, but others were as high inside as 10'-3" and the model photos of Proto cars seem to show that they're not.
I found the Hendrickson article from August 2003 and unfortunately there is no table attached, but there the photos also seem to show height differences.
But I thought those were channels (C-sections) on the diagonals, not Z-sections like a "normal" single-sheathed box had.