1981 Windshield wiper arm and motor

[cigars01]

I have a 1981 310 Vanguard. There are 3 windshield wipers. None of them work. There is power to getting to the motors. They look to be original and rusted etc. What brand and model motor do i need and how do I disconnect the motor from the wiper arm? I show pics of both. I cant see any clips or anything that tells me how the arm is attached in order to remove it other than taking the hacksaw to it. AFI makes some that look like it but how do I know which is the correct one?

Anyone with experience with this be appreciated.