A friend with an "oscillating cutting tool" (read "jigsaw") would be able to cut the amp section in 10 minutes or less. Any wood shop would probably do it for $20 also. It's a hell of a deal.. the 18" Ultimax is a beast, and that size driver with that much power in a sealed box would be phenomenal. Too bad it's OOS.
You could also just buy the driver and enclosure, then add a Behringer iNuke1000 DSP amp. You'd just need to install a Speakon connector on the box, which would be much easier than installing the whole amp. You'd save a couple of hundred bucks, too. Total maybe $700 for the driver, enclosure, amp, plus the Speakon connector, a couple of cables, screws, and acoustic stuffing. Maybe some paint, if you want it not to be hideous.