First of all, if you're trying to sharpen an older Japanese sword, please don't attempt it until you've truly researched the historical/monetary value of the blade.
That aside, one of the best sharpening systems I've tried to date is made by Lansky, http://www.lansky.com/sys_frame.html
which was originally designed for knives. The advantage this system offers is that it gives the user the ability to choose the angle he/she wishes to achieve, while maintaining that angle during the entire sharpening process. Write down the details of the settings you choose the first time, and you can at any time go back and resharpen at the exact same angle.
However, regarding potentially valuable blades, Japanese or otherwise, "hands-off" is the only recommendation I would ever make.
I hope that helps!