My 2004 Alfa GT 1,9 jtd has something between 150- 160HP, but the 1,9 jtd can handle 180 HP without problems.
There was an official 1,9 jtd version, only for the French market, with 170HP from the factory...
Milage is no real issue, if the engine is OK, a remap will do no harm at all.
Remember, brakes, clutch etc. will have a harder life, if you use the car to the max...