I don't believe that ssps got an aluminum driveshaft. I know that mine does not have one and I don't know why anyone would go from aluminum to steel.
They had heavier duty seat backs, the earlier models had reinforcing plates at the seat mounts on the floor pan. Ford later incorporated that into all production cars.
Bigger alternator with an external regulator, I believe that it is called a "Lesco" not sure on the spelling.
The silicone hi miler blue heater and radiator hoses.
Dome light doens't come on when the doors are opened.
You can check out
www.sspmustang.org and get alot more info there.