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Since it was built on a thompson action, I doubt you'll see one in 223, even more doubtful, you'd see a firing version up here (too bad, I think alot of geeks would love to have one)
There was a company that built a one off in 9mm with a 870 12guage on youtube:
I dunno, I can see a heavily modded version of the H&K SL-8 working a little, combined with an 870 on a drop rail that might work. Would cost an arm and a leg tho