Weird ? about small block pulleys

Your pulley configuration will vary depending on the engine's original application- i.e. a/c, p/s, etc. An a/c engine, for example, will have a larger w.p. pulley (edit: meant to say smaller, for an overdrive ratio); but in turn, an a/c water pump has fewer impellers... What it amounts to is it's a "system", so the component selection should be the one that most closely matches your current configuration/intended usage.
And by the way- don't mix and match pre-'70 and '70 and later pulleys- the offsets are different due to the early iron water pumps being shorter than the later aluminum water pumps.
You should have no problem switching pulley sets between a 318 and a 360, as long as they are from the same vintage as I noted previously.