Oh I assumed you had the D15B motor.
Looking at the D15B3 specs, the B18A will be a good gain in ft/lb torque:
http://en.wikipedia.org/wiki/Honda_D_engine#D15B3
However, it will be far from a direct swap. In addition to the axles, motor mounts, transmission, linkage... converting from carb to fuel injection will be done. (ecu, wiring harness, fuel pump, possibly fuel lines too.)
That's just the main parts, I'm sure there will be some more misc. items.
I think that is a lot of work for such a small upgrade in power.
A B16A (or any B16) or B18b would be more worth the work of the swap.