First Gen Camaro subframe welding

[jasonz28camaro]

I need to make a patch on my subframe on my 68 Camaro. I removed the motor and found gouges in the subframe from someone possibly dropping the motor on it or prying the motor up with a sharp object. See photo attacked. Either way i need to cut out the damaged area and weld a new section in. What thickness plate should i purchase to do this repair. I’ll also be notching the subframe a little for my new accessories and i want to use the same plate to do so.