Thanks.
Yes, it had canti's origionally.
The V's are XT M739, the origional V brake.
I used a braze-on front mech converter (Evans - £6). It converts a braze-on front mech to a banded version. Through that I put something similar to a barrel adjuster (Halfords - £2), of which the ID was drilled out to 3mm so that the teflon frame liner would fit into. From that there's a 2" prices of outer cable (to allow the essential amount of movement) into an Avid V brake metal tube.
The braze-on converter had to be ground down a fair bit to fit over the chainstay weld.
There are more pictures of it on my 'Klein Rascal' thread (see Carsten's post above).
It works well, it's going for a proper test ride tomorrow.
It's not particulary neat, but I got so fed up with messing about with rollers and various other idea's that I went back to my origional idea and it worked quite well!