[FatBoy]

I don't know what number it is, but I'm pretty certain it is 3/8" inside diameter.
The pipe comes out of the front of the pump straight into a 90 degree bend pointing up and towards the centreline of the car. The pipe then goes over the front of the diff and is tied to the steel brake line. The steel line is wrapped in a length of rubber tube at this point to prevent rubbing.
The steel brake line goes under the driver's side trailing link front mount but the fuel line goes over the top and sits inside the plastic triangluar cover for the trailing arm mount (I can take a picture of this bit if it helps). At this point, the fuel pipe is wrapped in plastic pipe to prevent rubbing (the plastic or rubber pipe is cut along its legth so that it can be wrapped around the fuel pipe and then held in place with either cable ties or wire).
The fuel line and brake pipe then come together again and follow the same route to the front of the car down the outside of the main chassis tube. They both pass over the top of the intermediate outriggers where there is a gap between the cockpit floor and the outrigger.
This routing is how my roller was supplied by Kirkham about 3 years ago.
I've just put some rubber washers between the chassis bracket and the fuel pump to try to cut down some of the noise the fuel pump makes. With the metal to metal mount as originally supplied, the noise from the pump really rings through the chassis, but I haven't tried it yet so I don't know if it is any better.

Did you sort out your brake lines to the reservoirs? You can see in the picture that I posted on that subject that a short length of aluminium is riveted to the inner fender to hold the pipes in place.

Paul