Mid '30s. I have the diagrams packed up. Announcement in the Erie magazine too.
Were originally door and a half single sheathed box cars built in the late '20s or early '30s. A few of the cars were converted to single door, single sheathed box cars which were numbered in the 84000 series in the '40s.
The original single sheathed cars had tongue & groove roofs.
Ted (you remember him, right?) sent me a photocopy of an actual blueprint of the original single sheathed cars from the builder (packed up somewhere). My recollection is that at least some of the original cars were built by standard steel, Keith Retterer offered a photo & Ted recently sold a copy of this photo on e bay.