Its very hard to believe that faulty plugs can cause overheating issue.
Overheating can be due to issues in cooling system.
Check temperature of upper radiator hose and lower radiator hose. Lower radiator hose shouldnt be cooler to touch. It should be hot.
If lower radiator hose is cooler than it means there is issue in coolant flow.
There are 2 possible reasons of coolant flow issue, air lock around water pump or thermostat valve, or a faulty thermostat valve that is not opening.
Air lock is easier to remove, an air vent screw needs to be unscrewed while radiator is topped up.
If thermostat valve is faulty, it needs to be replaced.
For knocking issue, may be high octane should be given a try.