A couple of other details for anyone planning to do the same.
I had a lot of trouble trying to source spacers. They seem to be unobtainium (at least in Oz)
So I made my own, bought a length of 20mm aluminium rod, cut into desired length, drill a hole down the middle with a hand held drill. I doesn't matter if you are not completely accurate, it's not a bush, it's a spacer.
The spacers you see in the photos above, between the guard and the cutting board are ~15mm.
There is also one with an 8mm bolt through it that goes right up through the horn bracket and has a nut on the top of it to hold the horn on. This one is about 20mm long.
Then there are 2 about 10mm long between the cutting board and the original plastic doofus.
See WW Ronin's thread for more details.
I am attempting to avoid cutting into the main fuel tank.
To that end, instead of running fuel lines from the TT tank to the bottom of the main tank I have run a line from the TT tank to the vent on the main tank in the hope that as the fuel in the main tank is used it will suck fuel from the TT tank.
When I get home from this swing I will test this idea.