Is this what you are referring to?
https://thirdgenauto.com/product/1932-53-ford-starter-to-oil-pan-reinforcement-bracket/
That is not an earth strap, is a structural support for front of starter motor.
An earth strap from the starter to an oil pan bolt serves no purpose. Your earth strap from engine to body is doing what you need for the electricity to get back to the battery.