mild street suspension question

ok, you used two different terms for your duster, rebuild and upgrade. lets address both.
as far as rebuild, after 38 years, your duster is going to have a lot of worn out parts. so those need to be addressed first. take care of your ball joints, pitman and idler, tie rod ends, and bushings. buy quality stuff where you can, as it sucks to have to do it twice, even when the parts are under warrenty. for a full rebuild kit, look at either PST or Just suspension. ive used both with fair success, though lately i have been doing stuff piecemeal with manufacturers i like. after everything else is up to snuff, check out the stering box and coupler. sometimes the box can be adjusted to get rid of slop, sometimes it can't. the coupler is a snap to rebuild.

as far as upgrading to turn, theres many options depending on budget and preference. i'll give you my OPINION on what should work well, but just remember, its my opinion, based on what ive tried and liked. it is not the gospel.
1. after a thorough rebuild of all the non-bushings (using my favorite brand, MOOG), buy an energy suspension bushing kit. fire up the belt sander and shave down the strut rod bushings by "i think" 1/8th of an inch. someone will correct me on this im sure. use 80 grit, it seems to work best on their poly. also, toss the upper control arm bushings (and remember to get the big ball joint control arms with your disc spindles)and install the moog offset ones. i wish i had done this on the current suspension in my duster, but you live and learn.
2. add the ADDCO 1 1/8 front sway bar, and a small rear. ive had good luck with addco, and the one for the 70 will clear the 73 calipars in the stock location.
3. upgrade to the 340 duster torsion bars and leaf springs. should be just stiff enough for the /6.
4. add a set of KYB shocks. theyre inexpensive, and work reasonably well.
5. if a poer steering car, swap in a FFI stage 3 box. i just finished mine, and LOVE it!
6. upgrade to 15 inch wheels. i use the wheels off a diplomat, 15X7. theyer cheap, readily availible, and fit right. i can fit a 235/60.15 front and 275/60.15 rear on my duster.
7. add subframe connectors. i did that, and it really helps. i did mine like the big block dart website says to.

except for the upper control arm bushings, and spring rates this is roughly what i currently run in my duster. i am still dialing in the alignment specs for my driving style, but it handles pretty fair. still think my wheel/tire combo is holding me back, as well as too soft a spring. but that should get you in the ballpark for minimum investment.

hope that helps
Michael