The front driveshaft was the only thing that went on mine, and the GTR shaft slotted in like a bought one The only difference between the two (being that the S1 Stagea carries the GT4 driveline, not the GTR) was a step down in diameter about 2/3rds of the way along the stagea version.
Depending on what end of the driveshaft is whipping around, your problem is either going to be the output shaft bearing of the transfer case or the pinion shaft of the front diff. The front shaft uni's are not supposed to have any discernible "play" in them, so you should be able to isolate the problem by hand.
Just be glad that you got the shaft fixed before you snapped a uni, they almost always kill vital gearbox pieces (and in some cases clutch and bell housings hey Leshy?) when they break loose and start flapping about under the car.