Rocketman's 1973 Road Runner
Fabricating the Rear Bumper Center Trim
My rear bumper center trim was originally made of some kind of hard rubbery material. It was totally wasted beyond any repair. I could not find it anywhere for any price and so I had to make a completely new one. Actually, it was pretty easy. Here are the instructions of how I did it. These instructions include the the approximate dimensions I used - but my car is pretty extensively reconstructed back there and the end trims are too. My dimensions might not be right for your car.
First, measure the length between your end trims as accurately as possible. Go to a plastics supply company (look in phone book) and get a piece of PVC plastic that is 1/8" thick by 3" wide and the length is 3/16" - 1/4" LESS than the distance you just measured. You will also need a piece of PVC edge trim also just a little shorter than distance you just measured. You can get it at most upholstery shops or online from Trimlok.
Take your 3" wide long piece of PVC and cut it in half lengthwise so you have two pieces 1 1/2" wide. The cut must be done on a 45 degree angle. I used a table saw to do this (perhaps the plastics supply company could do it for you). Then you will need to glue one of the pieces on top of the other so that both the 45 degree angles point in the same direction and the offset looks right. I believe the offset distance was about 1" but you should check for yourself. Ideally, the top piece beveled edge should line up with the bottom edge of your trunk lid, and the bottom piece beveled edge should line up with the corners of your end trim pieces.
Use PVC cement to do the glueing and you should clean the surface first with lacquer thinner or acetone. After you you glue them together then test fit them on your car to be sure everything still looks good. Then push the edge trim you bought over the back edge of your bumper. Next, position the glued long strip properly so it lines up with the corners of your end trims and each end has about a 3/32" - 1/8" gap. Once you're sure everything will fit you can glue the long strip to the edge trim using PVC cement and lacquer thinner or acetone again as prep. Let the PVC cement dry at least 1/2 hour. Once the PVC cement is dry remove the finished assembly and run a bead of liquid superglue along the bottom of the beveled edge between the upper and lower long strips. The superglue will wick into any gap there and act as a filler so it will look like one piece when you paint it. If necessary you also use a small amount of Bondo to fill any gap. You can also superglue the other edges for extra strength if you like.
Finally, sand the whole assembly and paint it to match the end trims. I did mine in silver and as far as I can tell that was its original color. I hope this helps. If you make one send me pic.