As a complete assembly, any front end fits any CT70 frame. Wheel assemblies are all interchangeable, too. You can reuse your handlebars with the K3. Your K0 headlight shell/speedo bucket will fit the later headlight ears, though it will be positioned a little differently. The hydraulic fork is a nice upgrade, over the K0 pogo sticks.
K1-`78 all use the same handlebar mount which, owing the revised "clocking", give a wider stance than the one-piece K0 top tree/bar mount used with the same bars.