That is weird. I belong to the NIZAN drift and drag club, and their weapons of choice are all Silvia's from 88 - 2002. All the SR20DET powered S13's, the S14 and S15 all have steel wheel T28's. The CA18DET's all a slightly smaller version of the T28 since there are quite a few different AR housings and wheel combinations. Remember T28's and T25's are very simular where as it is the turbine flange that donates the turbo more over than the actual size. Some T28's such as those found on the GTR are ceramic but, others are steel. I made a quick phone call to Francsis who lives and breathes the Silvia and he also confirmed it as did my renter who another siliva fanatic.
To my knowledge the only vehicle Nissan ever produced that use a ceramic turbo was the Nissan Skyline series, and they were T28's (really T25 size with T28 flanges) on the GTR, and the T3 found on the GTSt, GTS4 were ceramic, T3's GTS25-t's (R33) which used ceramic in the series one and plastic poly on the Series two.