I just thought that I'd pass this along. this is the Boss 302 that we run in PWC and IMSA, once the cars are stripped out and the cage is installed our cars weight around 3700 pounds, so they are pretty heavy. What we do..within the rules, we are allowed to change the upper trailing arm to an adjustable one, change the lower trailing arm adjustment points, this allows for a corrected pinion angle after lowering. The car has to be at least 4 inches off the ground, our cars are usually more. With regards to the front suspension we are limited to camber of around 4 degrees. The in general go to setup for most places is a 300 pound spring in the rear, about a 600 up front, the Ford Performance adjustable "blue" bar in the front and an 18mm or no bar in the rear. all of this rides on hi zoot Penske coilovers, but there are less expensive alternatives. We also use tire pressure as part of the spring rate scheme.
You need to throw out what you think you know about suspensions and sway bars, these cars really need to move weight around in order to handle and not punish the tires, here's an example of a car that set on the pole at the VIR 24 hour race, it led until the clutch destroyed itself, it was up against Porsches, Astins and BMWs.. This car runs lot's of aero, but on a 30 mph corner, it's all mechanical grip, aero really does not come into play in a serious manner until about 50 mph.
the IMSA car, that didn't have large aero, also ran a very soft suspension
Another modification that you will eventually need to do if you track the car, is to cut the shock tower to allow for more camber, the mustangs love camber. You will see that there is no shock tower brace, we don't use one, the cars are all seam welded and are very stiff. The roll cage helps, but we are not allowed to go forward of the firewall, or behind the rear suspension mounts in these cars.
With regards to aero, you basically have 2 choices, the IMSA package, or the PWC (big wing) package, both of these cars have been in the wind tunnel, what you CANNOT do is mix and match the splitter/wing packages. you get one, or the other, to mix them will throw the car off horribly, we tried removing the rear wing at Daytona to find some speed and it really didn't work out because we lost so much time in the bus stop.
One thing else that I would recommend besides the matching aero is to run suspension components from a single manufacturer, normally, we use Ford Performance because they sell their stuff in a "kit" form that is designed to work together, we don't use rear trailing arm location brackets but we do use an adjustable upper trailing arm that is not Ford sourced, the car is remarkably stock underneath, except for the coil overs .For the street, I would recommend against coil overs, good one will cost north of $5K and will need to be rebuilt every 20K miles, our Penskes are $10K for comparison. For the 99.9% of us we will never be able to fully utilize the adjustments to the coilovers although they do make it easy to change ride height. FR kit's can be ordered with adjustable shocks and struts that come with separate springs, for a street car this is a bunch more user friendly.
This is the Ford Performance track pack and is the exact basis for what we use on the competition cars. In some SCCA classes, we cannot use coil overs because of class rules, so this is the EXACT parts that we use for those cars.
I hope this helps you out on your crusade for better handling, remember, in these cars unless you have virtually unlimited tire rules, weight transfer is your friend, even though you may have been told differently over the years.
This car was the runoffs winner in 2018, barely beating the BMW, which finished on it's bumper, in 2019, the roles were reversed and the car finished in second spot, but it wasn't for lack of trying, the Mustangs have to run a tiny 275 tire with the stick axle so the BMWs definitely have an advantage. This is all Ford suspension track pack with coil overs.