66 C10 Hood Repair - large shallow depression at rear of hood

[TxCajun]

66 C10 Hood Repair - large shallow depression at rear of hood

I'm doing rust and dent repair on the hood of my 66 C10. At the rear center area of the hood there is a large shallow depression. The picture below shows a straight edge laid on top of one of the ribs at the center of the hood.

a. I wanted to confirm that these ribs should be straight and flat, i.e. not have this depression.

b. Any suggestions on how to go about fixing this? Because it is such a large, unsupported area, it seems to want to "oil can" back to this position.

Thanks!