Yes, Gen2 internals will fit in a Gen3 slide. Early Gen2's had a 90 degree ejection port and 90 degree extractor, Gen3 slides will have 15 degree for both, however a 90 degree extractor will work in a slide which has a 15 degree ejection port. Gen2's used non-LCI extractors with corresponding non-LCI spring loaded bearings, almost all Gen3's have used LCI extractors with corresponding LCI spring loaded bearings. So if you put the extractor from one slide into the other, you must use the corresponding spring loaded bearing with it.
I have no idea if a 15 degree extractor will work in a slide with a 90 degree ejection port, to my knowledge no one has ever tried it.