Certainly the physical component changing is no problem at all. Probably the biggest difficulty is figuring out how the donor S2 was wired. There are recent posts re rev counters that highlight this problem. There seem to be a lot of different variations of S2 instrument packs and of the consequent wiring that goes with them! For this reason, I'd be inclined to actually remove the instrument cluster from a scrap car, so that you could verify which wiring scheme it used, rather than simply buying a cluster off Ebay.
Chris