compression driver recommendations
I second the recommendation for the JBL 2430 Aluminum compression driver. This is about as close as you will probably get to the driver used in the new K2 speakers and it is supposed to be one of the lowest distortion compression drivers that JBL has ever built. The 2430 is available for around $220 and I saw that the 2332 is available for $68. Just a diaphragm for a 2445 or 2441 costs almost as much as the complete 2430 driver.
I'm thinking about a similar 4355 project with a pair of 2235H, a 2020H, and a BMS 4590 coaxial compression driver. I have a pair of 2380 horn but I may go with a smaller horn. One of my 2020H was damaged in shipping so I'm waiting for a UPS check.