If only comparing the bottom side, no difference can be found between (2166 & 2164, 4166 & 4164). If comparing the upper side, you can find 2166 & 4166
have an exclusive parts(fix position sensor for LightScribe function). So,
although crossflashing seem to be success from 2164, 4164 to 2166, 4166,
LightScribe is still not workable.