I'm not sure how an adapter plate could be made for this application. I bought a new bellhousing for my 3550 for only $125, and it is identical to the stock T5 piece except the bolt pattern. The stock bellhousing has provisions for either bolt pattern, but once one pattern has been drilled and tapped the other pattern can't be, as a couple of the holes would overlap. The Tremec mounts in the car the same, but the rear of the trans. casing must be trimmed and the front edge of the frame mount must be trimmed for clearance. I've got a Mark I, so I can't comment on the Mark II specific questions.
FFR2710: 400+RWHP, Vortech blown all Trick Flow 302, 3.27 IRS, Cobra R\'s, Tremec. Bodyman is finally ready for my car, Soon to be Lambo orange!