I have a 68 Dart sedan /6. Is there a way to put more "feel" into the
power steering system? What I mean is, how to put more resitance into
the steering wheel to make the car less "twitchy" at highway speeds.

See my response to your "How to improve the ride?" question -- those mods will help, too. Extra positive caster in the alignment will help. These P/S systems combine a very fast ratio with a very "disconnected" feel -- if you want better road feel and self-centering, you'll need to have stiffer reaction springs put in the steering gearbox. (A set of stiffer torsion bars will also make the ride less jiggly and tippy)

That's what I need to do right there. Do you have p/ns or procedure? Link to a site maybe?

Actually I should do a sector shaft adjustment before I judge it, but Im worried about overdoing it and wearing it out faster. How's your steering play, ballout?

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I've been calling it as i see it for my entire life and that's not about to change. Take it or leave it.

Firm Feel can do it, as can Steer & Gear. I used to have P/Ns, but they're buried in my info archive in Denver. Perhaps one of those outfits will sell you just the parts to do it yourself, if you're so inclined.

As far as I can tell I have very little steering play. What I notice most is
when driving on straight roads at speeds over 40 mph I have to make
lots of tiny corrections to the wheel to keep the car between the lines.
Like SlantSixDan said the feel is very "dissconected". Back in the day
everything I drove had this kind of steering. I guess driving my 91
Cavalier has got me spoiled.

My '66 Coronet V8 does the twitching routine and bounces all over the road, despite a rebuilt front end and stock alignment. The steering is so light, you can't feel the road at all.

Conversely, my '64 Valiant tracks as true as any new car, has good road feel, good handling and never bounces around. It's totally stock, has 13" tires and needs the front rebuilt. Go figure.

chech your toe - in should be about 1/8 inch ...less will be loose ...more will be tight...tooo much either way tires will wear quickly

Check for worn/loose tie rod ends and the other joints. My Dodge truck was that way too until I finally discovered a loose joint in the center link. Had to replace the center link and all was good again.

Just a thought; my '71 B-body power steering starting leaking internally around the little O-rings atop the steering box and caused really squirrelly steering - it boosted away from the center and was very difficult to steer straight; became nearly undriveable.

I swapped on another control with O-rings and the problem never returned.