Ha!!! I changed to '84 S cast wheels on my 78 GS1000S. Went from 17" up to 18" and from single front disc to double front disk. I can see though where you may want to drop to 17 for new low profile tyres because you may need a wider rim and have a width problem.
From what I have you will have a number of choices just watch out for rear disk brake placement and swing arm width.