Both D2 Racing and PSR have replied with more details, provided below. Please note that both mention a "supplier". In the case of D2 Racing, the supplier (TW Racing Parts) is from Taiwan. PSR provides the same exact specs; I am therefore concluding that TW is also their supplier. Also, as mentioned by Dr.Jeff, spring rates for Street version are far too high. I'll let you review this and let's talk again. The Australian $ equals approx. $0.77 US.
PSR Performance Suspension
As you'll see there are 3 different kits available.
Super sport - which we usually recommend for street cars. This kit has a front spring rating of 5kg/280lb and a rear spring rating of 7.2kg/403lb
Top sport - which is more of a firmer option. This kit has a front spring rate of 6.3kg / 353lb and a rear spring rating of 8.7/487lb
Race spec - for more Track use than street use. This kit has a front spring rating of 7.2kg/403lb and a rear spring rating of 9.8kg/549lb
These kits come as pictured in the listings linked below.
https://www.performancesuspension.com.au/?rf=kw&kw=Fi03+
D2
All prices are AUD and include GST.
There are 3 available D2 coilover models for the Fiat Bertone X1/9:
Street Version (
http://www.d2-race.com/conpage.aspx?dsn=1911&csn=1267) - Pillowball Rubber Top Mounts front and rear, spring rates 5.0/7.2kgmm respectively - $1999
Sports Version (
http://www.d2-race.com/conpage.aspx?dsn=1911&csn=1268) - Pillowball Top Mounts front and rear, spring rates 6.3/8.7kgmm respectively - $2249
Circuit Version (
http://www.d2-race.com/conpage.aspx?dsn=1911&csn=1270) - Pillowball Top Mounts front and rear, spring rates 7.2/9.8kgmm respectively - $2699
As I understand, the Bertone X1/9 is a McPherson Strut design so the front top mounts will provide camber adjustment.
Included is the 4 x coilover units, 2 x height adjustment spanners, 2 x damper adjustment tools and any other necessary fittings + installation manual.
Depending on the intended use, one of three versions of coilovers should meet your requirements for this very unique car.