Cutting down the factory valance is eazy-peazy. Easier and certainly
cheaper than replacing with the 'shorty' GM unit. As mentioned elsewhere on this forum, use an oscillating saw and finish with a sanding block or, with practice on the sacrificial piece you can 'flame polish' the raw end vs. sanding.
I used two widths of 3/4" painters tape down from the top as a guide for cutting, but just experiment with what YOU like.
Used GM metal skid plates on eBay all the time - generally $50 ea.