Peter,
The filler pipe I have(which was supplied from Warwick Harrison) was piece of rubber filler hose(genuine gm part), a piece of exhaust pipe with a bend(don't know the angle ) on the end and an unleaded insert to suit a holden fuel cap.
These days an unleaded insert might not be required as you can't buy anything else.
I read a post on another forum using silicon pipe for petrol filler hose. This fella cut a piece of the silicon hose and soak in a small amount petrol and after a couple of hours the silicon had expanded to twice the size.
Warren