Looks like an interesting thread in the making Richard. If your friend is pretty knowledgable then we may be dealing with some kind of custom instrument. Gibson made many flat tops prior to 1935, but to the best of my knowledge, no 12 strings until Erik Darling ordered two of them in 1960 for he and Bill Svanoe (remember "Walk Right In")
The "C" tuning would be consistent with how most players tuned their Stellas from 1910 to 1950 (big with blues guys, but mostly used in Mexican music) and tuning it up to pitch is a pretty modern concept (as you mentioned)..however you can get ANY kind and guage of string these days so if the neck isn't a total write-off it shouldn't be hard to put the instrument back in shape.