Spoke length for SA Hub mated to 597 rims?

[Siestabikes]

I would like to mate the rim in foreground (non drop center rim) to a Sturmey 3 speed 36 hole hub. What spoke length do I need for 3 cross. Both wheels pictured are fronts

 

[Siestabikes]

275mm both sides. i had a helluva time building this wheel. I wasnt getting enough twist between the 2cd and 3rd rounds of spoke lacing so the 3rd set of spokes were not reaching the proper spoke holes. i had to lace one side of the wheel first, twist the hub, then lace the 3rd and 4th rounds of spokes.