If by spacer you mean a crank case spacer (approx 10mm thick aluminium or plastic peice which is the shape of gasket)
you can put this on either size of the reed cage.
-the order you listed leaves the crank case volume as the per stock but increases the length of the intake tract, I havnt tried this personally as a longer intake length IMO is a top end hp killer (slight exaggeration
)
-however if you were to put the space on the engine side of the reeds you would be increasing the crank case volume while retaining your std intake tract length. which in most cases will slightly increase top end while slightly sacrificing bottom end.
