Both pads are identical, they are cheapy gsf jobs , I'm wondering if that's the problem? It seems to me either the pad or the spring is wrong. I think if the back edge of the pad were a different shape the springs would fit properly.
They do fit flush until you put the springs in when they are pushed backwards. The new retaining springs are fitted as they came off , I'm also using my housemates 172 for reference.
Giving up now as I'm off for a week doing the scally rally!