It sounds like you have a good speaker plan in mind. You'll need to find tweeters that crossover at 2kHz or below if you're planning to use the π midhorn. You might also consider crossing over to a 1" exit compression horn, because I've already worked out that implementation and I know it will work well for you. But there are lots of other good ways to do it.Maybe use the midhorn and compression horn, but then crossover to a supertweeter above 6kHz or so. Perhaps your Heils could provide top-octave duty. Keep us posted on what you decide to do. It looks like you have an interesting project ahead of you.