My silver solder came in today. It's Harris safety-silv 45, 1/16" wire. I also got some Sparex 2, which will go well for pickling the parts before soldering.
Next I need my flux (arrives next week) and some bronze bar to make bushings. Once that happens, I'll evaluate my plans for the end plates on this boiler. In addition to the resources already provided, I have a good book by Alex Weiss that contains boiler calculations. His boilers are much larger than the boilers I intend to make.
Jon