An overdrive transmission might get you there.
This is a good calculator for making those comparisons
http://www.onlineconversion.com/bigger_tires.htm

For driving comfortably at 65 and not just occasionally getting it up to 65 you may also need a rear axle gear change.

If you're then regularly driving that fast also consider how good and reliable your brakes are or are not.

To be safe might take more than just the "least effort"

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
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"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-