UPDATE:
Its been a while since my original post, but I did finish the Imperial Horns, mated them with a multi cell midrange horn driven with a JBL 2446h Tweerter was a JBL 2404h horn for the top end.
The Imperials currently have a Eminence Magnum 15 LF, 15" woofer, driven by a Hypex 501 plate amp with DSP.
I ended up selling the speaker system to a friend who had a large shop building and wanted an over the top system. The sounds very impressive in the building - Bass is very good - punchy with F3 of 34 Hz. I did not push the woofer to hard on the low end with the DSP, the response was normalized up to 500 Hz, crossing over to the mid bass horn.
The bass is Natural in the large space and the JBL horn tweeter working out OK, but the MID Bass Horn is is the star. 500 to 4,000 Hz, it's presents is awesome.
All Crossover slopes for the system was 4th order LR, keep everything in phase, the Hypex handled the time alignment between the bass and the Mid range driver. The Tweeter horn was physical aligned with the mid range driver.
It was a great project to build - even though it took almost 4 years to complete
The system is a few states away from me so I cannot just go around the block to make set up adjustment. I ran out of time during the initial set up. Another trip is planned in the future to tweak the system further.
The electronics for the listening tests was an original condition Harman Kardon 730 Twin, 70's receiver, a $5 Sony yard sale CD player and crap cables - Still sounded GREAT!