I was thinking the same. I'm still gathering parts for my build. Have a 6.1 and a 46RH for the 71 Duster but have started to hesitate.
Wouldn't a modern tranny with more gears be better?
Then it comes to size. To fit the 46RH in I need to do some cutting and fabbing a new support. Then I could cut a little more and make room for something better with more gears.
Or is there a slimmer multi gear tranny out there? Best shift-bang for the bucks? What options do we have?