Question about installing master cylinder on 68 dart

Hi,The master cylinder on the dark I was just bought started leaking. I picked up a new one yesterday and had a question before putting it on. On the back there’s a metal retainer held on with a bolt. I read the instructions that came with it and it doesn’t say if I remove that or leave it in. I’ve also got a boot and small rubber ring. It doesn’t show where that goes either. Any help I’d appreciated as I’d like to get this together before the high winds show up.

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