From memory the breather valve fits inside the valve chest cover. It can be fitted upside down because there are no markings on it to tell you which way up it should go.
There are two small holes along one of the long sides- these are oil drain holes and must go at the bottom and face inwards towards the valves. Similarly there should be a gasket with two cut-outs that should go between the breather and the engine block to allow the oil to drain back into the engine- make sure it is the correct way around so that it doesn’t block up the drain holes.
I hope that helps.
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