thats simple. you can press the pinion on the shaft easily by using a vise. the shaft normally comes out a little on the rear side. all shafts of this 540 or 550 series have a diameter of 3,17 mm (must be some odd inch unit) and the same fixing holes. For more security you can add a drop of loctite (if you want to remove the pinon after glueing, you have to warm up the pinon with a lighter or so).

regards
Helmut