Run out of attachments, but google search for:
vultures "patience my ass I'm gonna kill something"
and you will see how I feel!
I finally resolved the issues, used the two screw method to remove the double ended threads.
I figured out the chisel and hammer idea, delicately... but no success
My neighbour is most useful as an antique desiel engine mechanic, he goaded me on for the day, whilst I worried the header with a pair of mole grips, WD40 for about an hour or so.
I resisted his very persuasive argument to let him heat it a bit. and swore at the bike alot, even kicked her once or twice, but constantly aware that I may have to do this in the bush.
30 minutes continous worrying with the bigger mole grips, (I've been watching my jack russel doggie go nuts shaking squeeky toys to bits so learnt from her.) and many many violent epitaphs later, I managed to release the one pipe blixem.
A further 45 minutes and now three sizeable blisters later I removed the other blixem then the copper bits as well.
I am now the proud owner of new Yamaha downpipes and the wrong (but it fits) silencer. Incidently the yamaha parts may (or may not) be stainless steel, but they are black and are cheaper than anywhere else.