I have an EB V8 fairmont and was wandering what I need for a manual conversion. I already have the clutch pedal installed in the car. Is the 6 cylender T5 the same gearbox as the V8 one? Do I need to swap ECU's?
If anybody can shed some light on this I would be greatful

No 6 cylinder T5 is not the same. The V8 input shaft is longer.
ECU will need to be either changed , fooled with the resistor trick or a J3 manual tune installed.
Do a search this has been covered many many times before.