Hi Dave,
Can't help with the headers/mounts unless you show some pictures, I'm afraid.
Re: the u-joint, you haven't got hold of one of those CV joints that is approx two normal u-joints in length, have you? I know over here they came in some of the early Lincolns but maybe some snuck (sneaked would be the formal term) onto the TBird shafts. The output shaft of the trans had some linear needle bearings that were really entertaining to install, and said shaft would need to be swapped if you wanted to use a "normal" u-joint.
My E-M has the C6/Jag rear combo and it works beautifully
Or have I misinterpreted the question again...
Let us know a bit more,
Tom