Thanks for the pictures Rob, very helpful, I started the job, hit a problem, and reading Monte's words now they prove prophetic.
I think there is a reason the PO routed the cables the way he did and its because they are too short to follow the correct route.
I discovered Anton Largiader has (another) very useful page on BMW cables:
http://www.largiader.com/articles/cables/The cables I have are the ones ending 236 612, i.e 1007mm overall length, this part no. is listed as being for /5 to /7 with low bars, though it has the same spec as the 237 691 listed for pre 81 R65 with low bars.
Anyway when I tried routing the cables like Rob's (and some other routing's) the cables were too short at the carbs.
I never really confirmed it as I have nothing to compare with, but looking at pics of other bikes on here ( e.g. boycies)I think my bike has high bars, I remember some of you guys commented on the bars first time I posted a picture saying they looked high.
Here is a clearer shot of them:

So looks like for now I will have to revert to the "short" routing and source correct cables, i.e. 237 692 or 236 613