I've used both Key whiz and GP Whiz in different projects.
The Key Whiz is a keyboard encoder, seen as a keyboard encoder.
The GP Whiz is a gamepad device, seen as a gamepad with a joystick and some number of buttons.
I don't have either in front of me but the 40 pin headers (if you go that route) do not have the same "pinouts" exactly, no.
What exactly is the question(s) you are asking regarding the pinouts for the GP Whiz that are not defined within the document Randy supplies with shipment?