I have bought a rear disk brake, I'm gonna fit it to my S1 Basket Case, looking at the kit (I didn’t get any fitting instructions) but the master cylinder bracket side of things will need some fettling (on the website they said weld it to the frame struts) I think I'm gonna modify the bracket so that it can be bolted on instead.
Ref the 'knowledge' quick release rear brake cable, if he's not got any in, a suitable replacement can be found here
http://www.gsfcarparts.com/
For my other scoot, I went to the shop on Kirkstall Road, Leeds and purchased a VW polo hand brake cable, thick cable, nylon lined, extra long so it'll require trimming down...just the job
Mike