The one on top is between the starter the the block.. You can't see it. You just have to get a long enough extension to reach in there. It will be the same size socket as all the rest.
I didn't need any wobble sockets, but I might have used a universal on that top one if I recall. I used a 6" extension with the socket on the end to get to the bolt. Then the U and another extension so that I could get enough leverage to turn the ratchet....
At least that's what I think I did??
here is a link to the post I did on this very thing..
# of bolts on starter?