Oh cool. I didn't know that he was selling them. I know for sure that someone with a built D series transmission setup would want to keep it in the car instead of swapping it out again- this just increases the number of combinations you can run. Being able to keep your existing axle/transmission/linkage setup is nice, especially if you have some cash invested in it already. It also enables you to choose whatever engine you want no matter what transmission you have.
As for daily driven, I'm sure it would be fine. The RWD guys do this kind of thing all the time- just look at all the VW people using non-VW engines in their Beetles, buses and Ghias. They're all over the place. Intercrew used an H to B setup in their drag del Sol, and it ran low 11.2s in its initial shakedown passes.