Well,
Technically the springs themselves will fit and there are many more options for springs when you're shopping for a TBird. From what I remember, the upper mounting flange on the TBird shocks is quite a bit different than the Mark, so that may be an issue. I don't see any way of checking other than getting your hands on some TBird assemblies and verifying fitment on your car. If they do fit, I know many of the TBird guys have had good luck with the Vogtland springs. I had the Eibach progressive setup on my '94 Bird and thought the front was far too soft.
-Dom