The dimensions (bearings etc) for pretty much all the S/S arm Honda stuff is the same as far as I am aware. The difference comes in the width of the hub and the method of holding the wheel onto the axle.

The RC45 I believe is the same width as the RS250, but the threads are left hand on the RC45 wheel side (to prevent the wheel undoing it) and right hand on the RS250 (because the arm is the other way around). Not sure about the sprocket drive end, I haven't taken an RS apart....

For info:
RC45, NR750 across bearings is 70mm. Will confirm with RS250 later in the week when I take one apart.
RC30, VFR750, VFR800, NC30, MC28 are 65mm
NC24 are (reputedly) the same but I've never measured one so I can't say for certain.
I believe that the NSR150 is 55mm, but this is from the 'horses mouth' information so it might be wrong.