I have seen one where the nose of the cam was sheared off. Whoever did it welded the hub of the timing gear to what was left. Hope that's not the case with yours...

The gear is an interference fit on the cam nose, which is tapered. It is definitely necessary to use a puller to remove the gear. I use a small 3-leg puller and pull from the holes in the gear, carefully -- pulling from the edges stands a good likelyhood of cracking the gear.

There's a special tool for pressing the gear on, but it will usually go on far enough by hand for you to start the nut, which will press the gear on by itself. Use a shop rag wedged in the teeth between the gears to keep the cam from turning while you torque it to spec. Use Loctite on the threads.

Do NOT apply any force that pushes the cam rearwards in the block. There's a soft plug behind it that will surely pop out if you do this. The endplay is controlled entirely from the front once the nut is tight.