[HatchBatch]

First, great selection on image for show your point, those Singer, Porsche rally cars, great stuff!

I found a breakout image of the stock airdam on the internet. The dam itself is a flat piece that goes down, but there is that lip, almost like a spoiler, that could be like the splitters you are showing. Its an interesting thought to ponder how I could extend those while keeping them structurally sound and not look too poorly made (my fab aero skills are not quite at the level of others on this forum yet).