Different owners of vehicles here have had there wheel cylinders lined with stainless steel liners and have found after the time using aluminium pistons that the pistons start corroding and they seize up, it is a well known fact that aluminium and stainless steel do not mix, so you can either use cast iron or steel or brass pistons which would have to be made with stainless steel lined wheel cylinders.
Ian, could you provide some references on the piston corrosion issue? Especially actual experiences. Since nearly all pistons of recent vintage are aluminum, this could be a serious problem.