Nicely done! That will work very well. I put 850 sway bars (stailizers) on my old 600 15+ years ago. I can't recall exactly how I did it as I have long since sold the car. Your method of adding the support "bar" for the brackets is great. I think I welded mine directly on to the chassis.
Are you installing a bar on the front too? I think I adapted one leaf from an 850 to attach to the 600 spring so that there is something to attach the bar ends to.
Paul van der Heyden has some great info. on his website on sway bars. As I recall, he says that an 850 bar should work better than the type Abarth used. I have an Abarth (replica) set that I am going to use on my car.
Are you doing any chassis modifications? What else are you doing with the suspension? Do I see that you are using a rotisserie to be able to turn your body over? If yes, can you post a photo of it?
Gil
