I rode my DOHC 750F with those cheng shins for 50 miles. I have never been squirrley on a set of conti's, metzlers, or avons, but those cheng shins would get "funny" in even the most basic of turns. The P.O. who put them on had about 300 miles on them so they were well and broken in, but on the DOHC cb750 I felt they were a liability. The 1979 DOHC has the same rims on th 77-78 supersports and it was tough finding good tires for both my 78 750F and 79 750f. I eventually went with avons, although I would have preferred metzlers.
As for the comstar swap, most people don't like the look of the comstar rims and there really isn't an advantage to having tubless tires when so many more tubed tires are available. The only positive side to the swap is that you get to use the better brakes and can get dual disc on the front. If you can score a complete 77-78 supersport rear end (swing arm, rim, brakes) and a complete 77-78 supersport front end (forks, rim, brakes) the brakes make the swap worth it. Since the comstars won't work with your existing brakes using the later brakes would have been part of the swap anyway. The only thing not a bolt on with the rear disc is the mount for the M/C which you will have to fab and will need to be welded to your frame. Other than that it is pretty straight forward, it is probably not going to be cheap so if you can get a 77-78 supersport rolling parts bike and strip it of its parts that is your best bet.
Personally I ride the crap out of my K5 and it is bone stock, my only complant is the factory honda front brake sucks.
