Its the ECU and its sensors that determines a cars OBD type...

That said, most of the sensors and other OBD specific things (on Hondas) are on the intake manifold...

So if you take a D16Z6 from a 92-95 Civic EX/Si that is OBD I, and take an intake manifold from D16A6 and use the D16A6's PM6 ECU, you would be running a pre OBD car...

Likewise if u take the Z6 manifold and ECu install it onto the D16A6, and wire up OBD1 (the wiring is also different because of the sensors) youd be running an OBD1 D16A6...