Custom crank and rods would be a start. They also have done 1.6 20vTs as well. The engine is fitted to this [YOUTUBE]zd8kzEapvck[/YOUTUBE]
It is an Autocross buggy and I suspect in you can run either a 1.6 or 2.0 NASP depending on drive layout. So running a 'small' 1170cc engine may put this vehicle in the 2 litre class with some sort of multiplier, expect there is more power and torque than any NASP 2 litre! I am sure someone with more knowledge than me can give more details.
Normal 1.8T 06A block with custom small stroke crank. Hohenester also made these engines years ago in German touring car series. 1170= can run in 2 litre class.