the compression is low because of the piston size and the stroke, if you do the B16 head swap then you should also buy higher comp pistons.
i am not too familiar with the comp ratio of the B20 but i am assuming it would stay the same ratio once the head is fitted since B series heads are very much the same.
i do not know alot about the B series engines, there are alot of ppl on here that do. hopefully you get point in the right direction.