Hello and welcome to the support community.
You hit the nail right on the head when you said about the screen being replaced by a later 1.33Ghz model.
The 133Ghz (2005) models came with the same AirPort extreme cards at the PowerBook 17". These are module based and attached to the logic board. Your 1.2Ghz model had an airport extreme card under the keyboard.
The attachment of the antenna cable does have a completely different connector.
There are no adapters that I'm aware of.
Sadly the only way to resolve this would be to buy and fit a new antenna cable in the screen housing.
Personally I would replace the screen itself to the correct screen, using a secondhand screen that works.
It would be much easier to fit than fiddling about with cables in the screen casing.
The cable is too small and fine to cut and join together. You might be able to do that, but from past experience when the end came off of a PowerBook, it didn't join properly leaving a very weak signal.
Hope this helps.