Well all seemed to goto plan, torch if anything could get too hot right enough and had a tendency to blow the solder off the pipe, so once I'd sussed that and turned it down a good bit it was fine.
Drilled the old pipe out as suggested, brass being harder than the copper it was easy to feel when the drill had got to the brass, looked like the original had been brazed in which might explain why I found it difficult to melt out.
I have a pot of silver solder flux, used that on the pipe, the silver solder I got is quite fine, could have done with a thicker gauge I reckon.
Anyway anyone faced with renewing the pipe and not sure about it - go and give it a go I found it not too difficult, I also took the opportunity to reroute the pipe so less bends, probably where it's supposed to be