Japanese boards, yes - both blue and green boards are interchangable. (make sure it _really_ is an actual JAP board inside, though - I've seen cases where an Aisian board was swapped from it's original grey case to a green one)
Just look at the bottom of the B board, and if all 4 connectors are the same, then it'll work on any JP or US A board. Aisian boards have one connector reversed (you could probable swap them if you had an aisian motherboard, too, but it would involve unsoldering an re-soldering about 100 tiny-ass little connector pins, and would be a serious pain in the ass)
I hope this helps!