I finally got my hands back onto the NXA hub.

As you correctly state it is wider than the RC30 and narrower than the RC45.

It measures 67mm across.....

All Hondas from the humble (and rubbish)NSR150 to the NSR500v use the same hub centre diameter and the the same PCD for the locator pins or studs whichever they are fited with.

I tried the 45 axle in the NXA hub, it fits but requires a spacer to make it work, the drive hub bottoms on the splines. The 30 is to short. Could be made to work if it was the only axle in the world, but the right parts are the right parts.

Not sure if this helped or hindered, let me know if you want shots or more measurements