For reference, here's the relevant page from the workshop manual (it's a screenshot so I hope it's clear enough to read).
Mind you, I usually just leave the anti-rotation insert in the slave cylinder and then line up the rod by eye. I suppose, if the anti-rotation pin is loose, then you'd need to reassemble by the book to stop it dropping out, since it engages with the insert in the vertical position. (Although a spot of grease would be enough to hold it in place.)