Thanks for the link but, Ian seems to have dropped the conversion some time back - his site hasn't been updated on the subject since February this year - and I was hoping to find somebody currently able to do the work. No worries, I'll keep reading and perhaps think again about ordering a tube from somewhere in the US. With refills for a 7 Litre compressed air tank running around $6 and 88g Airsource bottes at $14 it's got to be worth persuing.