Better re-read the link that Guz posted.
GT is analog, GTP is digital. You need to add and splice wiring when putting a GTP DIC into a GT. The "higher end" GT's (bose, heads up, etc) had digital DIC's, but from what I can tell, they are the same as the GTP DIC.
The only direct swap is GT DIC to GT DIC.
I have two GTP DIC's for sale....Grand Prix GTP Digital DIC's
Oh, and they look totally different from the front.