To be honest I think you'll end up getting the best result doing the lot unless the new panel fit is rubbish. It looks like you've had a sill repair already so you might find something unpleasant underneath that can only really be repaired by taking the plunge and replacing the whole lot. Not a lot more welding required than just the patch repair.
Hi Rob, thanks for the reply. It's really hard to get your head around all of the panels, where and how they fit. I've found several exploded diagrams on the net but it is still a little confusing. So, if I'm understanding this, it's a whole inner wing PLUS the flange repair panel OR is the flange part of the new inner wing ?
The flange is part of the outer bodywork but once you've welded it on to the outside you'll probably find that the wheelarch below it is so shagged that there isn't much good steel to weld onto. If you buy both panels you might get away with welding on the flange and then using sections of the inner wing without having to replace the entire thing. You'll only really need the edges since the centre of the inner wheelarch is alright, it is just the bottom of it and the lip round the top that the flange meets, if you see what I mean.
On yours it looks like they've just welded a plate over that little jacking point that sits just in front of the spring.[frame][/frame]
You wont really know until you start cutting away how rotten it is, but theres a good chance on an older car it will be sounder as the metal was thicker. If it were my car I would try and repair the inner wing as thay are quite a difficult panel to fit and then add the new flange or the parts of it that you need. Dont forget when you are welding it that there is body solder over the seam that goes up to the back window, try not to melt this!