Well it is a bit hard getting anything done during school holidays but managed to temporarily install the brake mount so I can see how it will fit with the frame lock. First impression is that I should be able to mount the frame lock on the reverse side of the brake mount with some longer mounting screws or maybe the odd zip-tie!
The brake mount seems very secure even with just the metal hose clamps in position -
I am not going to drill the top mounting hole until the brake is installed and everything is in the right position. I have a habit of drilling things only to find I should have had the hole in a different spot!
The rear wheel also needs a bit of spoke re-tensioning / truing so plan on getting the that and the brake sorted all at the same time at LBS next week (when the kids are finally back at school!!)