I hate playing full backs/wing backs on their wrong side. Much easier to defend against (just show them the outside) and players on the wrong side naturally drift into the wrong position.
One reason Gallagher and O'Donnell have played well the last few games is because they are playing in their regular positions. The main reason McTominay struggled is that he wasn't. I understand the desire to get Tierney and Robertson into the same team - it's just unfortunate they both excel in the same position.
Clarke will know what we are up against, though, and he's certainly earned the right to pick whatever teams he thinks will do the business.