(1) To get started you'll need a Fiero hood, all Fiero hoods are the same, so any hood will work. The extractor vent panel is molded with the correct contour to match the hood perfectly. You'll want to set up in an area where you can make a mess without getting thrown out.
(2) Mark the outline of the vent panel on the hood. Center the panel by measuring to each edge of the hood. The rear edge of the panel should be 19.5" from the front edge of the hood at centerline. Make sure everything looks straight and then go ahead and cut it out. A muffler cut-off tool works well. Be sure to only cut through the top layer of the hood (about 1/8"). Peel the outer skin of the hood away to reveal the understructure. Clean off any remaining adhesive from the understructure. Cut a smaller hole in the understructure leaving a small ledge for the vent panel to rest on. The ledge should be no more than 1/2" on the front, but can be 1" or wider on the sides. The rear edge of the hole should follow the front edge of the trunk sealing surface. Use the pictures as a guide. You may want to cut some strips from the scraps and bond them to the bottom edges of the hood skin where the vent panel is not supported. This will prevent the adhesive from dripping through during final assembly, and will also create a stronger bond. As an easier (quicker) alternative I have also just backtaped the edges with duct tape and I haven't experienced any cracking, even years later.
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(3) Set the vent panel into the opening for a test fit. The vent panel should be flush with the hood surface. Add shims (tooth picks) under the panel to raise it if necessary. Spend a few extra minutes to get it positioned correctly now, and you'll save yourself a few hours when it comes time to do the bodywork. Trim any edges as needed to allow a 1/16-1/8" gap on all sides. The edges of both panels should be chamfered to create a "vee" about 1" wide and 1/8" deep. Remove the vent and prepare the surfaces for bonding by removing any paint or surface coating and roughing the surface.
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Note: The rear edge of the panel has been changed from straight to curved, so that it will be fully supported by the understructure of the hood, and so that the seam will not be visible from the bottom of the hood.
(4) Follow the manufacturer's directions to apply the adhesive. Apply the adhesive to the hood at all contact points. Be sure to coat all panel edges. Set the vent in the opening and apply enough pressure to seat the vent in the adhesive. Place a heavy object on the vent to prevent it from moving while the adhesive sets. The edges should be filled with adhesive and spread smooth with a plastic spreader or putty knife. Cure time will vary with brands of adhesive, but it will usually set up within 30 minutes.
(5) Once the adhesive has fully cured, you're ready to fill and smooth the edges. Polyester autobody filler will work fine. Apply enough filler to hide the seam and sand it smooth, then prep and paint.
(6) Finally, step back and take a look at your new Extractor hood.