A friend has a 1958 750 spider whose tach stopped working because that gear came loose,so I know that at least on the early cars,they're a press fit. I think it's a press fit for the 1600s,and later 1300s,but not sure.You probably know this,but the parts books don't show a part number for that tach gear,probably why you're asking.Also,imagine what a PITA it would be to machine that intermediate sprocket and tach gear as one part,just sayin'
Had one loosen into the WP once and drifted it back where it belonged along with stud and bearing mount to keep it there. It might be possible with a collet to grab it and slide hammer puller. No, never did remove one in place.