74 Duster 408 Daily Drivability with 3.73 Gears Vs Stock 3.21 Question.

As someone who used to daily drive a car with no overdrive and a 3.58:1 rear gear, I'm going to say it depends. Lower RPM on the highway would be nice, if your 408 has plenty of lower end grunt, go for the 3.23 gears. Another option would looking into different gearing options for your transmission and maybe have an overdrive 4th gear.