Maybe engine swap to C4 AAT?
Only TDI in C3 was 1T with 120 bhp.
I know one latvian diesel freak, at my age. He started with C3 fwd 2.5 TDI avant, tuned engine, after crash he bought messed up [in condition that Coxy would say it's worthless
] A200q, swapped a lot of parts from former A100 and also from C4, at the moment he have hybrid 2.5 TDI made up from parts of all three 2.5 10v engines, 185 bhp, god only knows how much torque, probably around 400 nm, of course, he's planning more
Average fuel mileage is nice as well - 6,3-6,5l/100km.