Thanks heaps, WG
I'd only be talking anywhere between 20 and 30mm outer diameter tubing. Not sure of wall thicknesses at this stage.
I've had a look at Bunnings, and they have a tungsten carbide pocket scriber, (but no pic) for $12.95. I think that might be it.
And yes, DUH, flame polishing!
I should know that! My little dragon should manage that, eh?