There are special Volvo tools, but you can get by without them just fine. I use a small 3-leg puller through the holes in the gear to remove it -- works every time.

Installation is easy if you can get the new gear on far enough to start the big nut threading. The nut will pull it on. If you can't, you need to prevent the cam from moving back while you do some light hammering on the gear, using a suitably large socket as a drift. Have an assistant pry it forward while you tap -- pry points are the fuel pump lobe or the distributor drive gear on the cam.

Use a shop rag stuck between the gears to keep them from turning while you loosen/tighten the nut. It takes a 1-1/8" socket.

While the gear is off, remove the cam retaining plate and inspect both sides. There should be NO discernable wear -- it should be completely flat. There's contact between the plate and the front cam bearing journal on the back, and between the plate and the timing gear on the front, so it's not unusual to see some wear. The thickness of the plate at those contact areas relative to the spacer ring on the nose of the cam is all that sets the endplay for the cam, which is measured in thousandths on fan inch. If you have visible wear on either side of the plate, the endplay is out of spec and you can anticipate it getting worse fast.

Replacement plates are cheap.

Use Loctite on the two retaining plate bolts, and on the big nut unless your motor has the locking tab washer. Torque to 100 ft/lb.