You can change only 1 mount.

No need to buy a new Engine Shock; test it ounce you have it off. If it turns out you need one you can get one and install it later.

I cannot remember what the Engine Shock Mountings look like but the are Expensive. So I would take a goood look at them when you get the Car Jacked up and see which end of the Engine Shock Mount needs to come off so that when you Jack up the Engine you will not stress it.

I would also loosen the main single Motor Mount Bolt that goes into the upper Arm from the bottom on the side you are not changing the mout on before lifiting the Engine so that you do not stress the good Mount.

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84 300D, 82 Volvo 244Gl Diesel