Just a thought.... When I fitted all the components from a Decathlon on to my New Ribble frame I automatically used the longer side of the spindle for the chain set, a triple Campag. The chainset was much too far out, so I turned the axle around and the middle ring was bang on line with the middle sprocket. In a hurry to finish building the bike I left it like that (temporarily!) with the left crank 1/4" further out. That was 4 years ago, I forgot to get a symetrical axle. If your axle is asymetrical can you fit it the other way round? It would perhaps give you a better idea what length to go for, before buying one and finding out it's still not quite right. Best of luck.