The 944 NA's are 282x20.4. The T's (early and late) are 298x28mm. What hubs do you have? The T(86 only) and NA rotors will physically fit on the early NA hubs, but because of the shape of the early NA hub, if you put a the 86 T rotor on there it will interfere with your balljoint.
If you have a 4 piston brembo caliper, you need a 28mm wide disk. If you have the sliding ATE's, you need the 20.4mm wide disk.
See here for some more details and pics:
http://www.vdubcustoms.com/Tech/tech_pbrake.htm
Lanner