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My frame's lower headtube dimension is 1 1/4" and is designed for an integrated headset. Are there any shims to change the steer tube to 1 1/4" or reducer headsets that will accommodate this marriage of parts?
When you speak of 1-1/4" is that the nominal size or the actual size. If it's the nominal size, ie. for a tapered (stepped) steering column than I don't expect that you'll have an easy time finding a reducer, since the bearing sits directly in the frame.
OTOH it shouldn't be too difficult to find (or make) a sleeve to fit the larger crown race, or possibly to find a crown race for the 1-1/4" bearing, with an ID to fit a 1-1/8" fork. So I suggest you focus your energy on enlarging the crown rather than reducing the lower head bearing. Start by contacting the headset maker, and seeing if they offer a reducing crown race as a stock item.