If your Question is how to achive a good chainline when moving the 42T to the outside of the spider,the answer is Bottombracketspindle...a shorter one.The good news is that manny old spindles are uneven,so it might work to just flip it.Or you can get a new Cartridgetype BB in the right length.
As far as new Cranks...most Cranks need their specific BB length to achieve 42mm Chainline.