Ok, so how much lighter is it?
Comparing like to like, ie, comparing a manual rack to manual steering, HemiDenny says his coilover conversion kit saves 29.8 lbs. That doesn't include brakes because you can go aftermarket brakes on either style suspension. I'm sure the RMS kit isn't any lighter than HemiDenny's. From the man himself Early A-body HDK to be released soon
Now, comparing a manual rack to stock power steering the difference is probably more like 60 lbs. But, that's not like-to-like, and comparing a power rack to a new Borgeson power steering box probably puts the difference back in the 30-40 lb range. Sure it's a weight savings, but it's really not all that much.
Yup. That is an advantage of the coilover conversions, and not a bad reason to do a conversion. But that's probably the biggest advantage.
Really? You're sure that Pinto suspension scabbed onto a Mopar chassis would handle better? Why?
Coilovers aren't magic. They are springs and shocks combined into one unit. That's it. Coil springs are not superior to torsion springs, and shocks are shocks. Both the Mustang II coilover design and the torsion bar suspension design are unequal length A-arm suspensions. There are some geometry differences between those two examples obviously, but for the most part they are the same basic style of suspension. With the aftermarket parts now available for the original torsion bar suspensions, you can tune the geometry just as well as you can with a coilover set up.
I've posted an itemized list of everything you need to upgrade a torsion bar suspension for handling several times. The price to rebuild and upgrade the entire torsion bar suspension to something comparable with an RMS conversion (ie, replacing the steering, full tubular control arms etc) is less. In fact, you can rebuild the rear suspension as well and still be less than the cost of the RMS by about a grand. That's like to like (manual steering), with all new parts, and even a bunch of fancy stuff you don't really need for a street car. You can absolutely do it even cheaper than this. Here's the break down...
Frame or chassis options for A bodies
I've got no problem with the RMS, HDK, Gerst or any of the other coilover conversions out there. If you need the space for headers, or just absolutely can't live with the feel of a worm and ball steering box then the conversions offer a nice option. Plus you can get everything shipped from one place and just bolt it all on, and there's something to be said for that.
But don't believe for a second that you can't achieve similar handling with an upgraded torsion bar suspension. Or that you can't make them at least somewhat comparable in weight if you compare like-to-like components. All suspension systems are a compromise, and the RMS is no different. It has its pros and cons, just like an upgraded torsion bar system does. But the coilover set ups are not inherently any better, and they have not proven to be any faster on the track for handling.