Master cylinder replacement different

Just got my new Raybestos MC to replace on 73 Dart Sport. Seems like this is either the wrong application (don't think so) or this is the new and improved version. Anyway, the plunger for the old unit appears to be a separate piece from the MC. The New unit has an internal plunger. So I'm trying to separate rod from old plunger without damage.
Do I have this right?

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