geoffj, yes the blurb said it was’nt compatible but: I successfully bodged a 160mm bb7 on mrs j’s slot dropout inbred. (not the current one with the funny washers, the one from the big bargain batch a couple of years ago with ‘normal’ slots/trackends. Diggerent brakes now so sorry I can’t do you a photo of what it looked like.
As I recall, the trick was to wind the fixed inner pad out (towards the rotor) a bit, and the moving inner pad in (away from the rotor) a bit, and then fix the brake cable so that the ‘arm’ of the caliper rests at 1/4 to 1/3 into its travel rather than going all the way back when you let go of the brake lever, as this is the bit that fouls the seatstay. I also wrapped a bit of helitape round the seatstay to fit and set it up, and in case of sudden cable failure.
It was pretty simple (I mean, I managed it!) and I managed to get the same travel and feel at the lever end as the normally-set-up front one. I also managed it on a 14″ one which I guess will have the smallest angle between chain and seat stays, and therefore tightest caliper clearance.