I have an old frame I'm converting to SS/Fixie. I have a rear wheel with the White ENO to help deal with my vertical dropouts. Sheldon says it has a 47.5mm chainline. I'm looking to buy a new ISO square taper BB and crankset (probably eBay for both) to go with. My BB shell is 68mm, and I see there are tons of Shimano cartridge BB's on the 'Bay for (I think) reasonable $$. There are different axle lengths, though, and I want to get one that will work.

Or do I have to pick the crankset first? In which case, looking for recommendations there as well. Not looking for fancy colors, or awesome finish. Just plain silver and competent (i.e. round).

Thanks for pointers!