The 160 should not cause a problem. Especially in a deep rim, any spoke end that would protrude above nipple won't matter. It would be a problem if you bottomed out the nipple and ran out of threads to properly tension the spoke, but only being 2 mm off that is highly unlikely. If you are still concerned, you can get a good LBS to cut and rethread the 260 to make it into a 258. There is a machine for this purpose that some LBS will have. Buy some extras. They will come in handy.