I can't tell from the photo, but where is that structure in relation to the mast? I don't know about what Ericson might have done, but I do know that quite a few Cal boats (Jensen Marine) used a mild steel team to support the downward mast loads. It is very common for this beam to rot out over many years and require replacement, which is not a trivial job.
I see that you referred to "structures" in the plural. Is there more than one of these? On the Cal boats there was only one, and it was located directly underneath a wooden compression post in the cabin that took the mast load for the deck-stepped mast.