Mike,
Here is how I did mine. I decided to mold the inner contour as I wanted it to be as smooth and fair as possible. I made a plaster splash of the hood contour and laid some glass on that to make a base for the plug. The shape was band sawed and sanded to fit the base and epoxied to it. Then sanded smooth, sealed with a two part paint, filled, sanded, spot filled, sanded again and painted.
The plug was waxed, and painted with polyvinyl alcohol and laid up with three plys of cloth/epoxy resin. I used carbon fiber because I had some left over from making the inner fender wells for my brothers streamliner. Standard bondo, sand, prime and paint for the outside.
It mates up with a plenum I made to fit around my injector.