Alex,
As Eddie says, the other mags have the spring loaded conical clutch. The one on the left had the center broken out of the cone, but otherwise they are both the same. The sheet metal cone dates from the EW (350 or 600) era. By the time of the mid-thirties Aero models the cone was a machined iron casting. If the tooth count and offset is right, there is no reason why you can not use them without the clutch mechanism assembled. Pity though, as when you need one these clutches can be hard to come by.
You bike should have the eight spline camshaft; the six spline came right at the end of prewar OHV production I believe. I have no idea why they changed. Of course, since then there is no telling what type of camshaft may have been installed into the engine. So you do have to check. You can see the end of the spline if you simply remove the retaining nut and washer.
-Doug