Personally I wouldn't spend the money on the coil-over mod., especially at the premium prices that particular vendor charges. Installing the front coil-over setup only won't help much except for the cool factor or are you doing more? There's a number of alternative vendors in Europe with the independent coil-over suspension like ricambio.co.uk, suderia topolino, Berni Motori, classicperformance-parts.com and one other one I can't remember. If going that route and replicating what Abarth did on the late model versions of the 1000 Berlina Corsas, I think you'd also want to install sway bars along with upgraded rear suspension, wider wheels, flared fenders, etc... You could use modified/stiffened rear trailing arms or go with the pendolare setup (replica) which does away with the trailing arms - very expensive! Not sure if you can even get a replica set anymore anywhere. Photo of it is below.
The coil-over suspension MUST have the upper attachment points upgraded and strengthened. Berni Motori sells the pieces as shown below. You could easily make these yourself. The upper bracket needs to be widened to accommodate the coil spring. With the coil-over shocks/springs, the spring force is now on the upper bracket and it needs to be well-secured to the chassis (see the photo of the Abarth). If you're going to be doing any kind of racing or hard diving on the street, I'd install the lower reinforcing plates where the swing arms attach. These are available from Berni Motori. You could make these yourself too. Mahlon Craft talks about upgrading the suspension on his website here:
http://users.ntplx.net/~kinukoyc/Pages/technical_section.html I installed the sub-frame boxing he mentions and bought Berni Motori Abarth replica pieces as in his photo below. A heck of a lot of work...
If lowering the car much, you probably will need the offset pins for the swing arms as available from Berni Motori in the photo. I'm using something similar ("trunnion adapters"). If you raise the swing arm attachment points, the "dimples" in the chassis (or reinforcing plate if so installed) need to be raised otherwise the swing arms with hit the body. You can see this in the photo of my reinforcing plate. Yes, more work...
One photo below is an original Abarth with the coil-over suspension. Note the modified upper bracket and reinforcing plate. I've done the reinforcing plate on my 600 Abarth project and it is also one heck of a lot of work! See the photo below. I'm using a lowered leaf spring (Abarth replica).