Nick, you're right. It is 48 possible orientation orders. I'm not sure where I got the 27 in my head.
mb, you're right too. It would be LPS for that orientation. MNI coordinates are most likely both LPI lrder and MNI space.

Because of all the confusion regarding coordinate order, AFNI packages will now be only 1-dimensional, something like k-space, so the physicists will like it. 1D programs will accept 3D datasets if they are followed by an accent grave, admittedly easier for our French users. For those that insist on 3D orientations, the new standard orientations will be RMA (rostral-medial-anterior) and MVA (medial-ventral-anterior) both of which show up much more frequently in a Google search and remove pesky left-right issues.