Your in a world of hurt at this point, about the only non-distructive way now would be to pull the engine. You might try a good pipe wrench again but since your likely to do damage to the adapter I would have a replacement on hand. They are getting hard to find new so you probably need to go through this again at the junk yard.
Yeah, I figured as much as far as planning on destroying the adapter. I may call the last local yard and see if they still have any XJs around.