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My guess is '56 since the right side swingarm pivot clamp is beveled but maybe early '56 since there is no gusset under the downtube. Same front wheel as '55 though. Pretty sure the ODS didn't come on the '55 since our team rider had a 955 and it it was still squishies for suspension. Does appear to be upgraded or a higher trim level with the xt front mech too.just another opportunity to be wrong eh?
My 855 has that extra thickness on top of the swingarm on the rt side and I bought it new.