I used the EDD spoke calculators dimensions for the DH-3N72 dynamo hub to calculate needed spoke lengths for the 3N80 dynamo wheel I built and it worked great.
http://lenni.info/edd/
Unfortunately so far as I can find Shimano documents dimensions for all of their hubs EXCEPT the dynamo ones in two documents on their web site. One covers IGH hubs and the other covers front and cassette hubs except for the Dynamo hubs.
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Gear Hubs Owned: Rohloff disc brake, SRAM iM9 disc brake, SRAM P5 freewheel, Sachs Torpedo 3 speed freewheel, NuVinci CVT, Shimano Alfine SG S-501, Sturmey Archer S5-2 Alloy. Other: 83 Colnago Super Record, Univega Via De Oro
Visit and join the Yahoo Geared Hub Bikes group for support and links.
http://groups.yahoo.com/group/Geared_hub_bikes/