Lowtimer - I'm inclined to believed your typo idea. Its only a 4 cylinder BUT there is a 235HP variant available.
One page in the POH states :- 0-320 4 cyl 160hp, but has been amended, the new sheet states:- 0-540 4 cyl 160hp.
A later chapter on engine limitations states :- engine : 0-320
So apart fom ripping the cowlings off to find the data plate, I think I'll accept its a 0-320.
Fortunately its the only mistrake I've found.