If you're doing a flange/overlap joint, you can use a common MAAP torch, acid flux and Harris Stay-Brite silver bearing solder and not worry about any warpage, etc. That solder melts at around 430 to 450F and then finishing the work when you're done is easy and quick. Sort of like working lead. Plus that solder is about as strong as a brazed joint. In fact on something like this, you can turn days of work into an hour or so. Good luck.
