I am tired of this bull, and all the misinformation. I bought a so called good final drive advertised on the classifieds and found it was worn out crap. I asked around and was told a 2000 Goldwing final drive would work. I have bought one of them and we will see. I will let it be known loudly and with certainty if they are interchangeable or not..
If you're talking about the splines in the drive hub, these are not sold new from Honda by themselves. You have to buy the ring gear with spline cup and the pinion gear as a set and it's about $450. The star hub that fits in the wheel is another $100 or so.
The Goldwing drive is not exactly interchangeable, but the flange cup and star hub are. You will need to press your spline cup out of the ring gear of your drive, and do the same for the Goldwing ring gear, then press the Goldwing spline cup into your ring gear, then reassemble.
Hopefully, you got the star hub to go with the Goldwing drive as used parts should be matched whenever possible.
If you're talking about the pinion cup splines (interface to the drive shaft) this and a drive shaft are available new for about $200.
The pinion cups are interchangeable with the Goldwing, but the drive shafts are not. The GW drive shaft is longer.