Lots of people have built π speakers using Altec horns, and the π crossover works very well in this application. I suggest that the 6dB version be used for flattest on-axis response, but that usually leaves the HF horn about 4dB louder than the LF subsystem, if it is a direct radiator or undersized horn. One way to get around this is to use the π cornerhorn configuration and I highly recommend this approach.