Aaahhh, now we are getting somewhere. (Oh, and by the way, Mike, I am the founder/President of Lateral Dynamics LLC, you'll be hearing lots more from us very soon, and yes we have a nice solution for the rear of your first gen F body at this time).
There are likely a couple of things going on with the link setups that you have ridden in. If the cars skamper about over bumps, it is likely that the spring rates and shock damping are the primary culprit, going "straight" over bumps is the easiest thing for a suspension setup to handle. Unfortunately, the majority of link setups on the road today, on typical muscle cars, are of the four link drag race type design, which is horrible for a street driven car. In the case of a four link, drag race or otherwise, there is an inescapable bind in the system in roll, there really isn't anything that you can do about it short of introducing compliance in the setup (such as rubber bushings, the best thing you can do for such a system). Most of the setups use rod ends in all pivot locations, which is murder on a four link setup. On a three link, it's completely fine, because the system is not overconstrained like a four link. The only decent (and admittedly poor) analogy I can come up with is a four legged stool. If you are on a flat surface, and all four legs are exactly the same length, you're good. If not, the stool will rock, because it is over-constrained, too many points trying to meet the ground at once. A three legged stool will never do this, it'll be stable and won't rock. Picture this as a suspension setup, going through roll, over bumps, etc, and you might be able to picture why a three link is "better" than a four link. Anyway, the drag race setups are not good at all for comfort, or overall handling, they bind, period. This is likely what you experienced, and would be cause for being skeptical for certain, I certainly would be.
And once again, I agree that the IRS, if done correctly, and made strong enough, is THE way to go, but it isn't all that simple. In the case of the domestic producers, well, they can't get the IRS right, except in the case of the Corvette, and the Viper. The new GTO, and the previous version Cobra Mustang both have serious issues that prevent them from being good candidates for retro-fitting. Just as bad, the new Mustang's three link setup is horrible, not the correct way to go about things either. Keep in mind that the domestic producers are far more interested in profit, manufacturing efficiency, etc, than they are in planting tires with 600 RWHP in all conditions. They could easily solve the issues, they have the talent, but not the economic desire. If you are dead set on an IRS system, I'd call the guys at Maximum Motorsports, who deal with the later Mustangs, and get the goods from them if possible, might be able to adapt to your muscle car? Not sure, but Chuck and his team are top notch, they race (and win), and are terrific overall. We're looking into IRS as well, but it will be at least a year before I expect we are ready to even prototype a setup, and at this point, I don't expect it to outperform our current setup. IRS is good, but only if all things are considered in the design, and this is not the general case.
And by the way, the reason that the new Mustang has a three link and Panhard bar, is because it is cheaper than the IRS they tried to put into the car. And to top it off, the three link they used, is basically, crap (not only my opinion, but the opinion of the engineers who were forced to package it in the an extremely short amount of time).
Mark
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