Hello again.
My standard system is all rusted and basically screwed. I've read that some after market systems badly effect running. Could someone please point me in th right direction? OEM headers are hard to come by so a stainless set would make sense but I don't want to ruin the bike. What header and can combo do people recommend?

Stay away from any of the new stainless steel ones you see on eBay they are very poorly made and will create huge holes (flat spots) in your rev range

Graeme France makes a stainless steel system, haven't spoken to Graeme in years so no idea how much he charges now failing that he may well have some good used stock ones or keep an eye out on eBay for a good second hand set if looked after properly they will last a life time, aftermarket systems come up very rarely these days but if you do find one post a picture on here for us to see first and we can advise you whether it's any good or not.
Si