Update! I added the following horn:
http://www.harborfreight.com/c...40134It was (is?) on sale for $9.99, so I figured 'why not?' I wired it to a separate circuit from the calliope above and mounted it from the center cross-brace that's in front of the radiator, pointed downwards. It ended up sounding like this:
http://hallert.net/images/airhorn2.mp3It was pretty good, but missing a little... something. So I picked up another one (same kit) and swapped out one of the horns with one from the calliope (a different note) and installed it in addition to the one above on the same circuit. It now sounds like this:
http://hallert.net/images/airhorn3.mp3All in all, cheap fun that gave me an excuse to crawl around under the car this week. :DI was crossing a railroad trestle recently in the car at the same time a pedestrian was stepping over the tracks without looking around to check for trains. I must have hit a bump, because I accidentally firmly depressed the button for the 4 horns. Whoops! My goal going forward is to avoid the temptation to use it to be an annoying jerk. As this goes against my very nature, I expect it will be something of a struggle.