For what its worth I was at the Glen 2 weeks ago for 2 days and in my opinion there aren't many heavy braking zones. You can carry a lot of speed even through the bus stop.
I don't have any experience with LEDs, but I learned that the M1, and GT350 use the nonLED turn signals due to limited space between the bumper and oil coolers. The GT LEDs are very large in comparison.
Super cool. I also have a black 2019 R and am your neighbor. I live about a mile and a half up the river in Seminole Heights. I recognized your location from the back ground in your pictures.
You could always add a Mach 1 10r80 cooler. The Mach 1 cooler is located in the front right corner of the bumper. The engine oil cooler is on the left front corner.
I have a set of non R GT350 springs. They are in a box and I could send them to your shipper.
To my knowledge all GT350s had magnaride. Even non r 350s.
Here is my Facebook market place add for them.
https://www.facebook.com/marketplace/item/1101172018364322/?mibextid=6ojiHh
My car has had that stumble since new. It also on occasion has that same stumble when coming up to a stop light or at a light in traffic. It used to be worrisome, but I'm used to it now. Mine is stock with the stock tune.