I think that I'd be more likely to spend $400+/- on a 760/7600 rifle and have someone cut the barrel back.

The Cabela's in LaVisita, NE, had an excellent 7600 in 280 the last time that I was there and they were asking (IIRC) around $550, which may be high, since Cabela's used firearms tend to either be over-priced, more often, or under-priced, much less often.