1st, this is my favorite mopar body style. However improving high speed aero and keeping the proper lines is got to be very tough. Your mock up maybe beneficial but as I suspect you already know, doesn't IMo enhance the visuals, which is probably not your #1 priority, but the car does look so nice. I don't disagree with your thinking, however, unless you plan on wind tunnel testing, it is all just an educated guess, that being said, I might give more difference to cosmetics, since it may not detract from your intents. I was on my ebody tossing around the idea of an at speed deploy able/foldable and/or air extended side skirts. Keeping it simple and reliable and non breakaway is my big hurdle, but would give streetable ground clearance, have little downside to appearance, but hopefully be effective when needed.

Short of recontouring your already gorgeous nearly finished cars sides into slabs, or adding FG covers, you have a tough hurdle here.

This you may not want to hear, but if this much concern is invested in aero on your car, I would ditch the OEM style spoiler and jump right to a swan mounted real multi element rear wing.

And the NC low speed wind tunnel runs about $450/hr.