I have one in my 74 duster with a 340 and 3:92 gears. Highway driving is fine, but in town there seems to be too much spacing between gears. There never seems to be the right gear to cruise in. Next summer I will try one of my regular 4 speeds to compare.
The good part is...it is a cheap alternative to the aftermarket 5 speeds. Still allows resonable around town driving and keeps the rpm down on the highway.