Firewall/Engine Bay Smoothing

My goal is to see as few wires and holes as necessary on this 65 Valiant. As such, I'm going to fill in several small holes on the firewall and inside the engine bay. I'm also replacing my rusted out upper and lower cowl. While it's out, I'm thinking of filling those two oval shaped holes, where body plugs normally go. I would then put about a 2" hole on each side for clean out and access instead. Any reason I shouldn't do this?

Also, this car had the front end partially disassembled when I got it. What mounts to the two small holes on either side of where the headlight wiring goes through the inner fenders? See third pic below.

Thanks!!

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