By coincidence, there was just recently a thread on this very topic (73 Charger torsion bars). Following are the comments I made on that thread:
In general, for handling, I have seen a wheel rate of about 10% of the front end weight of the car recommended (Andy Finkbeiner's book "Mopar B-Body Performance Upgrades discusses this, and is well worth the read). Not sure what the front end weight of your car is, but if we assume about 2000 lb it would imply a wheel rate of about 200 lb/inch would be a reasonable start. Your 228 lb/inch torsion bars are about 15% above this, so will ride a little harsher, but how you like your ride to feel is up to you. Handling books I have read, including Herb Adams' "Chassis Engineering" and Fred Puhn's "How to Make Your Car Handle" (both also well worth reading) warn against going with too high a wheel rate as this make the ride harsher and also adversely affects the handling. One reason to go to a higher wheel rate is to allow the car to be lowered without having the suspension bottoming out when hitting a bump, which is very bad for handling. In general, for the ride height you select, it is recommended to use the softest springs that prevent the suspension bottoming. Controlling roll of the car is best done with anti-roll bars (also called sway bars). Cheers!
From the 10% guideline, I expect that the 1.03 bars (about 195 lbs/inch wheel rate) will be a pretty good choice, the 1.06 bars (about 225 lbs/inch wheel rate) is getting pretty stiff. Your original bars, if they are 0.88 - 0.92 bars are only in the range of about 100 lbs/inch to 125 lbs/inch. I expect the 1.03 bars, at stock ride height. should clean up any header dragging issues you are seeing and you don't want to goo too stiff or it will hurt your handling. A quick read on the topic is Andy Finkbeiner's article "Torsion Bar Tango" at
http://arengineering.com/tech/torsion-bar-tango/. I really like the 73 Charger styling. Cheers!
