There is a lot of confusion floating around about chainline issues.
-The over-nut dimension of the rear axle and/or chainstay spread has nothing to do with chainline. Nothing. Chainline is measure from the center of the bike. The distance between the stays is precisely irrelevant.
-The Sugino RD crank, with a 103 mm BB with ring on the outside of the spider will give 45. I have always loved Sugino products; not sure what their rationale for this is. If you mount the ring on the inside of the spider (which is fine, but a little uglier) it will be 42mm. I would much rather do this than respace/redish a rear wheel. Bear in mind that if you respace it, it will not really be a flip-flop anymore.
jim
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Cross Check Nexus7, IRO Mark V, Trek 620 Nexus7, Karate Monkey half fat, IRO Model 19 fixed, Amp Research B3, Surly 1x1 half fat fixed, and more...
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SB forever