Why Carb and non OD a Gen 3?

I cruise my car around town, drive it in parades, and drive it to car shows within a two hour drive of where I live. Any further, I'll trailer it and I have no intentions of doing the Hot Rod Magazine Power Tour. Why would I want to go to all the trouble and expense of fitting some kind of OD trans in my Cuda when it already had a 727 in it?

Really good point. Comes down to what people want out of their rig.

I live 30 minutes from the "big town" of Spokane, Washington so almost any use of my car involves at least 30 minutes at 60+ mph. That's certainly within the two hour drive window, but it's enough for me to say I want OD. Even if I lived in a bigger town and ever got on the freeway, or maybe even a main road that had a speed limit of 50+ mph, I would probably want OD. But that's me, I just don't like the motor spinning at 3K rpm. Thankfully I am not everybody, that would be boring.

I might add that another "for me" reason is mileage. The better the fuel economy an OD gives means that I can enjoy the car more and drive it further. Not everyone has that limitation, and it is somewhat self imposed, but it is still a limitation for me. For some, economy is pointless because 10 mpg isn't much better than the 8 mpg the car gets without OD, making OD kind of pointless. And some rides are rough enough that driving it more than 30 minutes at a time is unpleasant, so why would they want to drive it more anyway. And for some the point isn't to drive it, it's to go fast or look good, all valid. But my goal is to make my Duster something I can enjoy as much as I can which means driving it all that I can.

To each their own.