Well about a year ago I was in the same situation with air horns.
First I ordered the red plastic ones that kolesy has on his KJ. I took them out of the package and was so excited, just to be disappointed. now dont get me wrong these things are very loud but have the same tone as the stock horn, I wasnt so happy. I packed them up and shipped them back.
SO i ordered some that were chrome a little bigger and (about 1") and the same thing. ( I've still got them, For Sale )
After that I started looking around, I work at a marina and a friend of mine hooked me up with a set he had on his 52' hatteras. sold them to me for 20 bucks. you could easily blow some ones ear drum with these guys
Theyre hooked up to a wolo air system, I like it better than a direct drive because it is way louder since its putting out about 110 PSI instead of 30.
also you can hook up an air hose and air up tires, ect.
Oh and theyre about 22" long. Youll get alot better tone out of longer and larger diameter trupets.