So I can guess the rear dumper for 156GTA are stiffer to fit the stiffer springs of 156 GTA (but why not the same for 147 GTA?).
I don't know why the GTA dampers are not listed for the 147 GTA, I can see no reason as shocks and springs are the same for both 156 and 147.
Finally, I can hypotize it'd better to mount 156GTA on my Alfa 147JTD if I couple them with Eibach Prokit springs.
I like to think that if you are going for the lowering springs, then fitting the shocks that, if anything, are suited to lower, stiffer springs, then they will complement each other better. If the original FSDs are suited to the softer springs of the standard car, it would be worth getting these if you intended to keep the cars original springs.
My question is: is this the difference? Is only that? Or maybe there is some difference on dimensions (e.g. holes diameter, holes distance, etc..) that do not physically permit to mount Koni FSD 156GTA on Alfa 147?
They will fit, I am sure of it. There is a guy on here who fitted 156 Sport Pack suspension to a standard 147, so this must mean all the fittings for suspension is the same.
The GTA is quite different in terms of wheels, tyres ... as for stiffening a car ... it is not advisable to go too far ... the whole vehicle will suffer ... such as dashboard ... another experience i have seen with my second car ... leading to cracks of the shell for some of my friends.
But the front dampers, the ones that do 90% of the work on the car, are the same. Exactly the same. Only the rear dampers are different, and the difference is only slight. Why would they make this change solely for the 156 GTA? What is it about the rear of a GTA that is so different from the rear of a standard 156 or 147. If you think about it, there is more difference between the rear of a standard 156 and standard 147 at the back - 156 has third section to the chassis fixed behind the seats, making it stiffer than the hatchback 147. In fact, the GTA Sportwagon has fold down seats, and no chassis brace behind them, making it quite a lot different to the GTA saloon.
I think the reason there is a separate part number for the 156 GTA is because it makes sense from a marketing point of view - GTA owners want something that is GTA-specific, even if it is only in name. And the reason they are cheaper is supply and demand and economies of scale, Larkspeed shift the GTA-spec dampers faster, as people with GTAs don't mind spending a lot of money on good dampers, this has pushed the price down faster than the price of the standard-spec FSDs
Just my 2p, my rear GTA-spec FSDs will be going on the car along with the Eibachs once the weather warms up.