I have sent Geoff (Walpurgis) a message describing your woofer enclosure project using an EMI elliptical drive unit. Geoff is the only one I know of who has some experience with these units.

He won't be able to test or measure the finished speaker, but he may be able to offer some advice. When the enclosure is finished, post some photos of it here, and try if possible to evaluate the internal dimensions, and hence volume.