Spindle Length and crank question
 

I am building an early 90's Specialized Crossroads frame up as a commuter/tourer/cross rig. As I am doing so I will be taking it from 7 speed to 8 speed simply because I have most all the parts required. It originally had an Shimano Altus c10 triple crank and a bottom bracket with a 122mm spindle length. I will be replacing the crank with a Deore Xt FC-M730 square taper. Should the new bottom bracket also have a 122 spindle length or should I just play around and see what gives me the best chainline?

I believe that the old spindle is the correct length for the new crank. You lucked out!

If you can afford it or you have different BB units lying around then I would try them out and see which gives you the best chainline. Spindle lengths work with one crank in mind and if you use a different crank then a different length spindle is most likely required to give the same chainline. The chainline of a given crank/BB combination is theoretical anyway and I've often measured the chainline of a setup to differ from its theoretical dimension.

Anthony