The frame number on those is on the left side of the frame as you sit on it, above the engine, not on the headstock. The front shock conversion is actually quite popular with the nutters that race them (yes, they really do, it's called plop racing!) A very easy job to fit a different headstock to one, just a tube tacked inside the main backbone, slide the headstock part over it, check alignment, then weld securely, job done!
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