The recesses are for a type of hood louver that AMC came out with, similar to the 68 Camaro with the chrome pieces on the hood. For strength and durability I feel your best bet is to use fiberglass mat with the proper resin and hardner...Rough out the opening with minimum 80 grit paper and apply your matting and resin. Sand as smooth as you can and apply a minimal amount of filler over top for leveling purposes. I would then block the entire hood with 180 grit (aftermarket fiberglass parts have tendency to be fairly wavy, especially any AMC parts I've bought, not as big a market as the big three). After you have the hood straight, prime the entire hood and finish blocking with whatever grit (320 400) the paint manufacturer recommends.
I have several AMX's and I have found anything aftermarket fiberglass AMC is questionable at best.
Hope this helps