I know it's too late, but go to Mike's XS 650 Parts and look at their brake stuff. They have replacement parts for the XS650, and Yamaha used the same 7/8" handlebar fittings on most of their bikes, at least from 1970 through 1982. I've replaced all of my handlebar controls with new ones from Mike at very reasonable prices. They have parts which are usable by other Yamaha Classic bikes, although they aren't identified as such on the site. They also have replacement, shorter cables for your bike, now that it has Clubman bars.
One reason it corners better now is that your weight is more forward on the bike, since you have to lean forward more than with the stock bars. The back wheel has enough weight on it; the front "sticks" better with more weight but may be more likely to cross up when you're in sand or on wet pavement, so watch those conditions until you're used to the bike's new handling.
Hope this helps ....
Steelburner