??? Joking apart, I think it depends on how much extra horse power, mild to wild and whether you wish to keep vehicle fairly original.
Wikipedia has this:-Fiat-Abarth OT 2000 Coupé America: introduced in February 1966, it was based on the 850 Coupé but powered by a two-litre engine.[15] It differed visually from the 850 Coupé in having a barred grill between the headlights, a split front bumper flanking a spare wheel which projected forward below the grille,[15] widened front and rear tracks and wings, and a vented front bonnet. The 1946 cc twin cam four-cylinder produced 185 hp (136 kW) and could propel the car to 240 km/h (149 mph).
Maybe an Abarth version twin choke carb and inlet manifold, also a freeflow exhaust manifold and silencer will wake it up quite a bit.
Not sure if I would want to do 149mph in the Arbarth OT 2000 version!