The 2 different stays aren't compatible. If you run the newer stay, you can't run the older gauges.
You can modify one the old generation to fit the new gauges, horn mounts and inners, provided you have the wrecked / bad stay from and old generation bike. You'll need it to cut some mounting brackets off and weld onto the other.
For bolt and play - get the proper generation. 86-93 or 94-06. Its much easier.