What Daryl said.
Those references will point this out I'm sure, but a silver/tin alloy (like Force 44 from Brownells: 5% silver + 95% tin from memory) will be stronger/better than tin or lead/tin solder. The added advantage is you can choose to hot caustic blue the barrel group if you choose; not recommended if the solder contains any lead.

Temperature of the melting point is not really relevant IMHO.

I don't think anyone would ever recommend silver-solder or brazing temperatures for laying ribs on a double.