Go to http://icelord.net/bike/ and download pdfs of the Sutherland's and Barnett's manuals, and check out the chapters about replacing spindles and replacing spindles with cartridge BBs. Both will show you how to figure it out, and have tables of data on JIS and other apindles, and on the varieties of cartridge square-taper. It'll probably be beneficial to put the parts you have back together so you can get an initial set of measurements.

It's pretty involved, and makes me think that LBSs can do no better than guess if they haven't tried to sort it out.