The stroke on the B16 isn't long enough to provide about 2.0 liters of displacement if you bore it out. Also, the B18 motors have a taller deck height than the B16 so you can't just pop a B18 crank into a B16 block. You would have to install a deck plate to do so.

Think about it this way. It's cheaper to buy a B18C block and resleeve/bore to 84 mm; than it is to buy a B16A block, B18C1 crank, deck plate, and resleeve/bore to 84 mm.