Your '81 KZ750 came with a cross-wedge automatic cam chain tensioner installed from the factory. If it does not have one, then it has been replaced. Seems odd for only 6000 miles. But with the age of the bike, anything is possible. You may want to check the cam chain for tension by removing the cam cover and checking the slack. You can tell if the tensioner is working this way before buying parts.
1981 KZ750H2 - V&H 4-1 pipe, pods, jetted, clubmans, homebrew rearsets, 18" rear wheel and more.
Parting out a 1982 KZ750H3 to fund future projects
2 other non-Kawasaki motorcycles