My advice as a professional mechanic would be to bite the bullet and take it to a German car shop. I don't know where you are, and I suppose Australia is kinda big, but I could recommend one in Melbourne. There are alot of things you can do on a 124 chassis by yourself, but this isn't one of them. Your don't necessarily need special tools, but you need professional tools. You should have every length extension possible as an example. If you round out the allen heads on either the tandem pump bracket or the fan clutch, you are in deep dodo.
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