Can you do me a favour PCooper before you fit the cables. I know the size of the barrels already, but can you measure roughly, within a few mm, the length of the inner cables. Just the cable from where it comes out the barrel to where it just the other barrel?
I'm going to try and make some once I source the right barrel clamps and outers. I'll post the results and step by step guide when I make them. I'll also let you know where to source the parts used. There's got to be a cheaper DIY way to get around paying Yamaha the princely sum of gold, silver and small children.
Cables can't be that hard to make to the right length.
Your help would be greatly appreciated.