Colin,
The Nardi conversion that was offered was called the Variante 1005, which I have fitted to my Coupe.
It consisted of larger liners and pistons which took the capacity out to 1721cc, a single twin choke Weber carburettor in place of the original twin carbs, and an Aurelia type of air filter.
It`s aim was to increase the torque figure rather than the power output, as the early 1500 Coupes were criticised back in the day for their lack of torque.
Hope this helps.
Bob