No problem. Every PCIe power connector from your PSU has 6+2 [in configuration where you can just detach this extra two pin and use it as a single 6 pin connector.
So after removing your 770, install gtx 1060 and put this 6+2 pin connector the only 6 pin par and leave the other two pins side. Check some youtube videos like "PCie Power Connectors Explained"