Hi PBB,
I think you're closer to the truth about weight savings than others have posted here, although doing away with the centerlink and Pitman arm also help with the weight savings. But again - 80-100lb worth: impossible.
About twitchiness: after thinking about this a bit further, I believe there are two ways where I can see that an R&P setup might be twitchier than the equivalent recirculating ball steering arrangement:
1.) To achieve equivalent Ackerman correction requires that the R&P be mounted further back in the chassis than the centerlink is now. This means that as either wheel encounters a bump and is deflected slightly rearward because of the compliance of the LCA bushings, the bumped wheel will tend toward a transient toe-out condition.
2.) Since the R&P configuration is lighter, it also poses less inertia for a wheel to overcome when it encounters a bump, so the yaw acceleration in response to road irregularities will be higher. Remember that road irregularities create fore-aft forces on the wheel, and the centroid of these forces, if taken to be the geometric center of the contact patch, create a moment about the steering axis whose moment arm is roughly equal to the scrub radius. As we reduce the scrub radius, we reduce the upsetting moment created by road irregularities. But unfortunately, the scrub radius for the A/G body from the factory is ridiculously high (about +90mm,) so - no surprise - the stock design is twichy. (Nowadays, the design norm is not to exceed +25mm of scrub radius, but this also relates to the matter of torque-steer for FWD cars.)
There are two solutions here, I think:
1.) Reduce the scrub radius, or even make it slightly negative.
2.) Tweak the Ackerman and/or bushing compliance to create toe-in with a bump input (or under braking, equivalently.) But, this is somewhere between difficult and impossible to do without creating other problems, so really, we come back to scrub radius.
With these changes, you won't need to touch caster, but admittedly - the changes I'm talking about represent major surgery for the front of the car, which is why I've believed for years now, that the right way to an R&P conversion is to completely redesign the front-end of the car.
Best,
MAP