1965 Dodge Dart high RPM issue

Original rear axle ratio was in fact 2.93 with 225 engine and automatic transmission. You may still have that ratio, or someone might have swapped the rear axle assembly for a later 2.76 unit. Since both 2.76 and 2.93 are between 2¾ and 3 turns, you may want to count quarter-turns of the driveshaft (easy, just count each rear U-joint cap as it comes parallel to the ground while you turn the lifted tire through exactly two revolutions). If you count exactly eleven quarter-turns, it's 2.76. If you count closer to (but not quite) twelve quarter-turns, it's 2.93.

2.76 instead of 2.93 will make the engine run slower at any given road speed, but smaller-than-stock tires will make the engine run faster at any given road speed.

Tired/sagged engine and transmission mounts will make the engine noise a great deal more noticeable.