These were a very limited production run of about 50 drivers or so. I believe the motor parts were similar to the HC, but machined out for a 4 inch coil.
Specs are:
Conservatively Rated @ 2000 Watts RMS
4 Inch Coil
Pole Vent
Specifications:
Fs: 31.0 Hz
Re: 1.14Dvc
Qms: 4.14
Qes: .517
Qts: .46
Sd Cm2: 810
Vas: 87.7
BL: 12.14
SPL 1W/1M: 88.9
RMS: 2000W