66 Mustang 289 2 barrels over heat

Hello my 66 mustang 289 over heat after driving 70 MPH for about 15 to 20 minutes . Then the engine has tapping noise and loss power as well. The engine run very rough once that happen. If I drive below 60 , I can run it all day. once the temperature reach 3 quarter of the way then the engine sound very rough.. I took the radiator to the shop to clean it out as well as replace thermostat. New water pump . Does it has anything to do with the valve ? About 6 months ago , I toke my car to the mechanic and was told one of the cylinder has a low compression. He said it might need a valve job 6 months to a year from then. Also is it better to have the engine completely rebuild rather than just get the valve job.. Any advice would be appreciate..... thanks....