Hi Thomas,
I've spoken to our drivetrain people this morning, they looked after M-Sports Grp 'N' propshaft needs for some years so know the cossie's very well. The joint cannot be purchased seperately, as I said in the earlier posting they converted all the 'guibo joints' to normal flanges. The rear flange for the box is available off them but this is not a ford part. To completely fix your problem i would quite happily have the front end of one of our old props converted and post you a replacement rear flange for your box if you have someone who could fit it that way you do away with the guibo joint. As I said before we ran this set-up on rally cars with no adverse effect.
Regards
Ian