This is really a newbie question, but I need help telling if I have a 742 or a 489 casting. My problem is pretty simple, I need better highway gears as I will never see the track and only use my Dart for a cruiser. Using the Richmond Gear rear ratio calculator, it says I have around a 4.56 in the rear. That would explain my 45mph @ 2500 rpm readings, but I need way different gears for my purposes. I know it can be hard to get anything higher than 3.55s, so I may end up running taller rear tires in addition to the gear change. Currently I am running 215/75/14s in the rear. Any hints on how to identify the rear would be helpful. Thanks!!