Repairing fenderwell coutouts.

Happy Easter FABO... Quick question as I finally start to get some body issues resolved. The P/O had fenderwell headers in this Duster and I'm going with the 440 and schumacher headers that wont require these holes. I'd like to either repair them (I have the removed pieces) or maybe replace the while inner fender (I've read that might be difficult). Any thoughts or tips on this?

Thanks as always,
Dale