I'm looking at replacing the oval exhaust tip with a twin one, any advice or links to any on eBay. Loads to choose from but not sure which to go for. Many thanks.

Are you welding it on yourself?

If you are still on the standard back box I would be going to your local Longlife/powerflow/custom stainless steel exhaust place and getting a back box made up rather than welding a new tip onto the old mild steel back box :)