Stainless steel, but I will be making some for my friend and I'm considering using 6063 aircraft aluminium and anodise or powdercoat finish afterwards...
I have also planes for a front tow hook with mounting on the absorber ( that means no drilling into the car, just take the bumper off and bolt it together in the position you want to. In the middle or more at side... ). I will be making it from the mentioned 6063 dural, which has the best specifications available. Anodised finish off course
I'm about to buy a set of xyz supersport coilovers with upper pillowball mounts, height and stiffnes adjustable. However I won't install it onto the car till spring ( no point of having it in winter ) along with the adjustable rear camber arms ( probably D2 ) and some other stuff.
If successful, I will post the results here