Here's why:
* Engine Mounts: The 1.9L engine's mounting points will almost certainly not align with the existing mounts in the 1.8L GT chassis. You'd need custom engine mounts fabricated.
* Transmission: The transmission used with the 1.9L engine might not be compatible with the 1.8L GT's transmission mounts or drivetrain. You might need a new transmission, driveshaft, and potentially differential.
* Wiring Harness and ECU: The engine's wiring harness and ECU (Engine Control Unit) are likely incompatible. You would need to extensively rewire the car, or potentially use a standalone engine management system – a very complex undertaking.
* Exhaust System: The exhaust system of the 1.9L engine will likely not fit the 1.8L GT's chassis. A custom exhaust system would be necessary.
* Cooling System: The cooling system (radiator, hoses, etc.) might need significant modification or replacement to accommodate the larger engine.
* Bodywork: Depending on the size and placement of the 1.9L engine, you might need to modify the car's bodywork to accommodate it.
In short, while technically *possible* with extensive engineering, fabrication, and mechanical expertise, it's a massive undertaking far beyond a simple engine swap. The cost and effort involved would likely far exceed the value of the resulting vehicle. You'd be better off looking for a car with the 1.9L engine already installed.