1973 Duster 340 Torsion Bars - recommendations

Degrees? No such thing. Bar diameter is increased to raise the spring rate.
If your adjuster is all the way in, your front end height should be sky-high even with wimpy 6 cylinder torsion bars. Chances are you have them installed wrong, not indexed properly.
The bars need to be installed with the control arms completely relaxed- this means loosening the nut on the pivot pin, and removing the bumpstop. Back off on the adjuster bolt as far as you can. With the control arms as far down as they go, grease the sockets and bar hexes and slide in your torsion bars and install the clips. Now turn in your adjusters until the hex is roughly even with the bottom of the control arm, you should feel the tension build as it loads. Now set the car on the ground and finish adjusting your ride height, bouncing the car repeatedly between adjustments. Now tighten your lower pivot pin nut and reinstall your bumpstop. Recheck your height after logging a few miles.
And get a factory service manual- this and everything else you could possibly want to know about your car in in there. It's the best money you can spend on your car.