I think the factory prototype Legacy originally flew with a turbo-normalized Lycoming IO-360.  It had good performance at altitude (i.e. up near 18,000 ft) but was a bit disappointing in takeoff and climb.

Tom,

 

I also had a flight in the Legacy with the TIO 360.  It was very disappointing in lower altitude cruise, too.  Later, after a flight in a 550 powered Legacy, the difference in performance was quite significant.  Thus, there are no 360 powered Legacy RGs around today.