DO i NEED A NEW MOTOR IF THE FREEZER PLUGS KEEP BLOWING?

You should listen to your mechanic as the freeze plugs will rust through and leak as will the radiator, It will cause more damage driving it hot and will cost 3X's as much if it blows the headgasket from overheating. You can get another opinion from a shop near you here http://repairpal.com/ford-repair-in-philadelphia-pennsylvania

If your engine still runs good and you do not have anti freeze or water in your engine oil, then you can just replace your freeze plugs. Since your engine overheated (caused by a low coolant level from your leaking freeze plugs) then you need to replace the thermostat. If your radiator is plugged (meaning the coolant is not flowing through it) then yes your radiator needs to be replaced also.