I am not a bike mech, but as I understand it, basically you would need to know the chainline for your crankset and also for the rear cog. If for example the rear cog is 45mm and the front crank is 42mm then you need to move the crank out 3mm. With a symmetrical spindle you need to increase its length 6mm. If the crank's 42mm was achieved with a 103 then you'd need a 109. Shimano UN54 are available in 110mm. That'd put the example off by 0.5mm. If the crank chainline is greater than the cog's then you need to move it in. This was a problem with a thread on another forum I read about the RD2 crank, someone had a 42mm cog and the RD2 was 45mm with a 103mm BB. Maybe there are some spacers that can be put in the back to move the cog out.

As I understand it the Sugino XD cranks do have a 42mm chainline with a 103mm BB. I think they are cheaper too. They are 110BCD.