If I could restore any UJM the Z1 would be at the top of my list. If you find one today, you'll pay top dollar for it. Great aftermarket parts support, not so much from Kawasaki. I can't believe all of the parts I can still get from Suzuki for the GS.
The GS was given to me by my Uncle that bought it new in 1978. It had set in a dirt floor lawn shed for 16 years. While not worn out, around 12,000 miles on a working odometer, corrosion had taken it's toll. So did street racing, the crank was twisted bad enough that I could visually see that 1 and 4 were not at TDC together. That was a common problem if ridden aggressively. That has been taken care of. The GS crank is pressed together since it is 100% ball and roller bearings. The Honda uses plain insert bearings like what you would find in your car. I was thinking Kawasaki's of the same era used ball and roller bearings, but I have never been inside one. Yamaha XS1100, I don't know what crank bearings they use.
Nice Kawasakis Fastgame, I rode an FJR1300 for 5 years and read that the Connie was a rocket. I'd like to ride one someday. This past summer, I traded the FJR for a Victory Cross Country.