All of the 2WD out put shafts I have seen on a 4L80E , they are all bolt on style shafts.
The 4x4 shafts are different.
The E brake tail housing design of the 4L80E will require the whole tail housing , brake and yoke.. these parts are all application specific.
This brake assembly is quite large diameter and may not easily fit under the floor of most cars.
Dont worry how old you are... it is the mileage on your body that adds up.