I hear you Randal do you think they are installed as needed or are they supposed to be specifically installed. It looks to me like the early models used 4 and the later used 2 only in the front part of the engine bay. What strikes me is that the aluminum disks are so much larger than the area they rest on and that they are slotted to fit on later. Moreover, they range in thickness a little. It is probably no big deal, but to me it looks more like an afterthought as opposed to an engineering design.
Steve