ZFs had either 2in or 3in, but since they are stub shafts you can swap them out easily. All NAS R380s had 2in outputs I believe. The cross over to 3in inputs on LT230s was in 97 IIRC (you would have to look it up) which was the same time the ZFs switched to 3in.
BTW it is not bigger, it is just the splines are longer. The shaft on the R380 is the same size and spline count.
*not legal advice*