Hemi Swapping a perfectly good 70 Duster

Power Tour has been a bucket list item for me as well, but even this year's new West event was a long ways from my home. Part of why I want an OD in my car is the idea that maybe I can take the 3 weeks off it would take me to get there, do the tour and drive back. Really want a car that can cruise comfortably for hours on end.
Could always just throw a 2.76 gear in it and roll! Honestly, that's likely what I would do if I were to put that many miles on the car even with the OD. 75mph at 1800RPM, yes please.