My thoughts at the moment are to dummy it up using 100mm pvc so I can work out the required tube lengths etc and then replace it with metal. Did have one thought later that car exhaust tubing is pretty thin even at 100mm ID, and would even be lighter than the heavier grades of pvc, so will look into that with the exhaust shop up the road.
Thanks for the advice re the alloy tube Bird, will look up the supplier when I've worked out the required length.
Interesting threads on the SS 80x400 Netwolf, given me a few other ideas, thanks mate
Glenhuon