I am running 4.30's with 30" tires and I have been thinking of going to 3.91's as I was hoping with my 493 it wont slow me down any. But my 63 goes just over 3700 lbs so I assume it weighs more then your Dart. I cruise at 60 mph turning about 3200 rpm and the eng actually seems to love cruising at that rpm. So I may drop gear a little one day myself to see what happens. Ron