I think we like the idea of flipping SR2 better than SR3 for the same ghost beam reasons as PR2 is better than PR3.  There isn't very much free space in the BS chamber, and if we flip PR/SR3, we have to deal with green ghosts as well as IR.

The flipping SR2 case seems okay to me - flipping either one of the SR folding mirrors gives us a slightly better g-factor than the design with infinite curvatures, and flipping SR2 gives us slightly better mode matching to the arm than the flipped SR3 case, but more importantly, there are fewer ghosts to deal with.  I vote we flip SR2, not SR3.