On my CR, I used Carrera coil-over shocks and a spring that fits the coil-over on the bottom but widens out to fit the normal MII upper spring perch. I think they call these helical wound springs. You get most of the benefits of coil-overs, like adjustable ride height, but don't need to alter the CR frame/chassis. The lower control arm needs to accept a coil-over versus the regular spring and shock. I used tubular control arms on my car.
I don't know if these units are still available as I bought them 20 years ago. What I can say is that 20 years and 36K miles later I'm still very happy with the setup. I think the spring rate is 500lbs. which works great with the iron block/aluminum head 5.0L motor in the car. Great handling but still a good ride.
I can take a picture and post if you're interested.
Just looked on Speedway, they still sell them: QA1 version,
http://www.speedwaymotors.com/Mustan...cks,35903.html Carrera version is $100 less.