Just remembered something else that might help. The outer race (the ring with a tapered bore that goes into the frame headstock) is different top and bottom.
The lower one (this is CB650 I'm talking about) sits slightly proud of the headstock when pressed fully home, so you can do that by tapping it into place (squarely) with some wood or plastic to protect the face.
The top one though is in a deep counterbore which means you have to drive it down into the headstock, and being tapered there's very little material to press on. I had a brass tapered piece made up that fits inside the taper of the outer race, with a hole in the centre. With a length of studding right the way through the length of the headstock i just tightened up a nut on the end to pull the top race down into place. It kept it nice and square, made sure it was fully seated into the bore, and the job was done in no time without any chance of damage.
You're welcome to borrow it. PM your address if interested.
Phil