I have a 68 dart with a 318, 4 speed manual, and 3.21 rear ratio. The car has a rear axle, K member, and suspension out of a 73 duster. I feel like at 45 or 50 mph I should be shifting to a higher gear but I am already in 4th. It is not a race car but I do some highway driving. The question is, would it be a mistake to swap to an OD 4 speed . I would be disappointed to go through the trouble of swapping the tranny only to find out it was a big oops. If anyone has done this and can give me your thoughts on this I would appreciate it greatly. Thanks in advance.
