Don't worry about the plastic cover plate, it is just to keep rain water and leaves from getting to the deep spark plug holes.

At a minimum, you will need new head bolts and a head gasket. Once off, check the head for flatness - it should be OK. This is also a good time to replace the valve seals, all 20 of them. And if you have a good machine shop, get the head cleaned and inspect the valves/seats.

Use a lot of penetrating oil on the exhaust manifold bolts, they tend to get rusty and you don't want to break one of them.

Use Volvo's RTV to glue the cam cover back on. Think about replacing the cam seals?? And mark the cams, intake and exhaust so they don't get mixed up.

Have fun with the project!! Summer and extended daylight hours are a good thing.
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My back feels better when I sit in a Volvo seat