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If you plan to swap in a Standard 4-Speed Transmission, fourth gear is Direct, as in no different than Third Gear in a 3-Speed manual transmission, or Drive/Third Gear in a 727 or 904 Automatic Torqueflite.

You would need a an Overdrive Transmission to bring the RPM down at freeway speeds. Higher continuous RPM does accelerate engine wear, though you may be able to live with that.

Swapping to Taller tires works similar to swapping in, say, 3.54 or 3.23 rear axle gear ratio, but off-the-line performance would suffer a bit as well, and there are practical limits on how tall a tire you can fit in your wheel wells.

There are lots of great Gear Ratio calculator applications available, wherein you input rear-axle ratio, transmission ratio (1-to-1 in high gear for a Standard, non-overdrive transmission) along with Tire Diameter which will calculate Engine RPM based on Speed in MPH.

You can run the numbers to determine what combination would produce your desired results, though it is always a compromise.

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