Kevin,
I have no experience welding and only some experience soldering. I've sweated copper pipes with a torch and repaired sending unit and carburetor floats with a soldering iron.
The soldering iron is an electric model with interchangeable tips. It has a 20watt and 40watt setting.
Is this the type of soldering iron you would use to repair this flange? How do you clean off both mating surfaces? Emery cloth? Wire wheel??