I importing a 1968 mustang coupe 289 Was wondering if it will run properly on unleaded fuel or need lead additive mixed with the petrol The engine was rebuilt few years ago?

A 1968 Mustang 289 engine, even if recently rebuilt, was designed to run on leaded gasoline. Running it on unleaded fuel without lead additive *will* likely cause damage over time. The lead in leaded gasoline lubricated the valve seats. Without it, the valves can become worn and eventually fail, leading to a very expensive engine rebuild.

Therefore, you absolutely should use a lead additive when running unleaded fuel in your 1968 Mustang 289. Many reputable brands offer these additives specifically designed for classic car engines. Make sure you follow the instructions on the additive carefully regarding the correct mixture ratio.

Failing to use a lead additive will significantly shorten the lifespan of your engine. The cost of the additive is far less than the cost of repairing or replacing the engine due to valve seat damage.