You have the cranks, do you already have the BB's? If you do, then just put them on. If the chain line is off far enough for it to be a bother, then you will know at that time whether you need a BB with a shorter spindle or longer spindle. Trying to figure out what spindle length to get when you are dealing with square tapers in a situation that isn't just remove and replace with same will drive one nuts.
If you have the square taper BB cartridge already, then you'll know if it works by just putting it on and seeing if the chain goes straight back to the cog on the rear. If it's got a bad angle on it and the chain comes off the ring or cog when you pedal, then you'll need shorter or longer spindle for your need BB cartridge. Maybe go to a bike shop or co-op and see if you can just scrounge some trashed squared taper BB's to see about the spindle length.
These both are IGH or just a single cog on the rear?