[V8] gearbox swap questions (not what you might think)

[brat boy]

Im interested in the 5 speed auto found in the late 90s a8 and a6 cars. ive noticed that the fuel economy on those 4.2 cars are way higher than what Im getting with a 3.6 and 4 speed auto. I think it would making driving on the highway would be smoother as well. I think the swap is possible because the 4 and 5 speed autos were both offered in those cars according to wiki. my questions are:


will it fit or will there be a situation with the driveshafts not fitting?

does it work with its own computer or is it tied into the efi?

Im hoping somebody around here knows these boxes a bit. thanks!