I purchased the lower valance from Firebird Central. Eight bolts hold it on and the bolt holes are already in your car, though the threaded u-nuts may not be. This piece is not pre-drilled. You will need to drill the mounting holes in the valance and fit it to your car.

Anyhow, I didn't use the piece I received. It would have worked, but I didn't like the way it fit. What I did instead was use it as a template and made my own from 4" PVC schedule 40 pipe. It took awhile flattening out the pipe, but after that things went quickly. The panel itself is flat and 1/4" solid PVC. It's going to do the job of closing out the radiator. I also installed the upper closeout panels too.

Back to the store bought fiberglass panel though. I think it would be better to sell these oversized and the buyer has to trim to fit. Back in the day our cars were pretty much the same size, but after 50+ years dimensions change here and there.