That Flipper door (where the cat is exiting) is the idea of what I've been toying with... and the outer edges could overhang the solid mount side sections by about an inch each side. The ride height of the car, as well as considering the OD of tires, will have an effect on how low the front spoiler(s) are to the ground. Another idea is to attach rubber edging (such as from drywall-to-floor flexible molding.. hardware store item...) to the bottom of the spolier... and it would be flexinle and more-so replacable if/when ever needed from hitting the ground, etc.... lots of road race cars use it already (comes in ~4"-6" or wider). Without having some flexible bottom edigng, its just a matter of time, guaranteed, that the solid spolier will get damaged.. along with the valence panel and probable fenders. Virtually all of the TransAm past race cars suffered that damage... many pics showing it on the web.... even more current active cars, too.. I strongly suggest to be careful with the "solid spoiler's" distance and... have the additional and desired lower extensions done with the flexable rubber edging.
Also... how about incorporating air ducts for brake cooling? I've been considering adding them into my factory plastic front pair of spoilers... the typical shop/floor vacuum ends will work... see from Sears, etc... 1-7/8" or 2-1/2" diameters... and the hi-temp brake cooling hoses are avlbl from race shops, as are ducting.
PS: Beef up the front TBs to be stiffer so to further prevent front-end diving (and lifting)... especially having your car with the BB engine... you'll want avoid diving into the pavement, etc, as much as possible (the factory TranAms pro race cars (Posey, Gurney) all had beefier TBs like ~1.4 diamater... so... consider installing up to 1.24 (like mine are and I love them!).... our factory hex size is 1.25"... Firm Feel can make you the 1.24 TBs.
