I had the exact same problem. My engine ran well, so I wasn't ready to tear it apart until I could afford to. I used a 1/8" Carbide drill to drill through both the kickstart lever and shaft. (I made several attempts with a HSS drill but the kickstart arm and shaft are pretty hard). Run your drill slow and use oil to lube the bit. Once through I drove a 1/8" roll pin through. When it comes time to replace the assembly, I can simply drive the pin out with a punch.
To date, this fix has worked
Matt
1982 Z50R
1979 Yamaha DT250