Radar,
At one time I thought about making the top link easier to adjust like you. Even thought about using one of those cranking side links like mentioned above. One problem I encountered, especially with my heavy boxblade, is that the link was super hard to turn with the implement off the ground. So it always had to be off the ground and not only that, but no pressure on the top link ... which is not always the case, (depending on what kind of tilt I had it on). Sometimes it turned easily. Sometimes I'd have to use a prybar to get enough leverage to adjust it. Anyway, the point is a manual adjustment became a PITA. I was constantly getting on and off the tractor to get the adjustment right especially when smoothing. It actually became a hindrance because I would tend to say that it was "good enough" just to avoid adjusting again.
If your Kubota has rear remotes on it, you'd be better off getting a hydraulic top link. I know you don't want to hear that, but the difference in ease of adjustment is night and day. Even for hooking up, it's a snap. You'll be a happier tractor dude and life will be a lot easier every single time you need to adjust the top link.
If you don't have rear remotes then RobJ is right. It will be an expensive add on, but still worth it IMHO.