@ M_V have you seen this? http://www.sturmey-archer.com/files/catalog/files/307/PART%20LIST%20-%20X-RD3.pdf This shows the axle as being 177mm.
Seems like those 177mm axles are the rocking horse shit of the Sturmey Archer world. There's maybe a more readily available 160-odd-mm axle that might work...
@TheShipwright started
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@ M_V have you seen this?
http://www.sturmey-archer.com/files/catalog/files/307/PART%20LIST%20-%20X-RD3.pdf
This shows the axle as being 177mm.