They might have been designed for those RPM's but that was back when 55 mph was the general speed limit. And even then, a 3.23 gear and 205/70R14 (E70-14) was only spinning at 2575 rpm at 60 (5 over).
I have a '91 Dakota w/ a 318 TBI motor, A500 and 3.55 gears and it cruises at just over 2K rpm's at 60-65 mph and jumps to 3K when it kicks down to 3rd to pull a hill (gutless motor, 5.9 Magnum swap in the works). Going back and forth makes it pretty apparent that 3K suck, no thanks. Not to say I haven't killed OD for a long hill and then forgotten to turn it back on and not noticed. So certainly you can get used to it, but when sampled back to back, the lower rpm is much nicer.
I run an A833OD in my Duster with a 3.21 rear gear and 25.7" tires. Runs at 2k rpm at 65, pulls the hills without needing to shift down, works well on the highway. Even fun to drive on the side streets, pulls hard enough.
From about '92 or '93 until '98 I drove my Duster as my daily with about the same setup, 3.21/A833OD, but with a slightly taller 26.1" tire. This was with a low compression 360, Isky Mega 270, TQ, HP exhaust manifolds. Worked great, probably a touch more fun that how it is now since the current cam in the car is kind of on the smaller side.
If it were me, I'd run the Purple Shaft cam, maybe find a way to tone down the compression, use the A833OD with some 3.23 gears and enjoy the car for what it is. Should make for a fun all around car.
