Guys,
If my memory serves me, the K-501 from the 450 was a 1 inch exit and was a tractrix horn(? Roy might have to correct me on this). The K-506 horn was from the 456, had a 2 inch exit and was a tractrix horn. The K-506 might be hard to find in the used market. Guys like JoeyB, have a hard time parting with their KP-456 cabinets.