Post more pics...pull a drum if possible. I kinda think those may be '37-8 cable brakes with Ansen conversion.
Don't have access to it right now and these are the only pics I have, but I'll see if I can get more.
I'd use stock 39-40 or 42-48 backing plates before using any old conversion. Sell them to someone who "needs" them and offset some of the cost of the correct parts.
If A they would be 11", and I don't know where the iron ribbed drums would come from... these don't look A. They have Bendix looking hold downs showing and what looks like a rotated cable outlet bulge showing...but those pictures are very limiting.
I was thinking the ribbing looked more like '36 brakes; but the axle bell is later. The pictures I have seen of the Ansen conversions showed Huck wheel cyls with a hole drilled next to them to access the adjustment notches, these were '32-'34 plates, maybe later plates were done differently.
The chevy Huck cylinders were used because they could both apply the brakes and adjust the shoes, important since that had to happen in the same place on the '28-34 conversions. Others like the one pictured above have the stock adjusters at the bottom and cylinder at top, so did not need Huck type cylinder...but I have NO idea what they used. The ansen conversions were available as full kits for all the various models '28-34 and were heavily advertised everywhere for a long time. They must have been fairly common, yet I have never seen more than scattered fragments.
Yea, it would be interesting to see whats inside the drums the OP posted; but most of time the thread just kind of ends with no further info. Always neat to see what was done in the past.