OK, figured it out by looking at the metal plate at the back the pad where the anti-rattle clip rubs up against the metal. The thinner pad was on the outboard side with the wear indicator located at the bottom, same on the other side. I think the inboard pistons are just slightly further out which made it difficult to put that pad back in. What I'll do is loosen up the caliper bolts then insert the pads, then tighten down the bolts; that should push the pistons back on that side. They are 100 series pads but may be replacing them with EBC 7000 Greenstuff pads soon (100 series).