Regarding Tory Werne's comment on the Williams C1200 Dbl Chainring set and "catalogues tell me 46/49 and 47/50 were the valid combinations (C1232 ringsets)"
the Classic Lightweights UK website recently posted a new page on Williams cranksets, the differences between them (see table entries for C1200 and C1232 cranksets in this instance), and chainring availability.
see
http://www.classiclightweights.co.uk/
Peter
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Peter Brueggeman
La Jolla California USA
pbrueggeman(AT)ucsd.edu