2 speed to 3 speed wiper swap.

Hi all, I've got a 2 speed wiper on my duster that doesn't work, and a 3 speed switch and motor sitting around, so thought why not swap? What I want to know is do I need any other parts like different wiper linkage, or wiring? Or is it a straight swap, my initial thought is it looks like a straight swap,,,but surely that's too easy. Anyone done this swap on an A-body?