My silver solder knowledge is from investigation only. Silver solder comes in a variety of melting temperatures starting around 800 degrees F. and going to 1800 degrees F. Jewelers will refer to silver solder as soft (1100 F.), medium (1300 or so) and hard (1800). Using silver solder is really brazing. A conversation with a Jeweler might get you started in the right direction. Stay-Bright is known to melt at exhaust temperatures.

However I did purchase some soldering rods (Model AL-3 4043 Aluminum Soldering Rod) from Lowes and was able to stick some aluminum together with a propane torch. The trick seems to be in understanding the melting point that cannot really be seen. Cleanliness is also a problem. And I found clamping to be a problem. The AL-3 has a working temperature of 700 to 750 F, which should be enough for exhaust work.

Let us know what you find.