Retain 3.0l injectors, fuel rail, ecu, gearbox ecu, and measure the exhaust manifold to see if it is the same. I suspect that the manifold is narrower/smaller, and so is the rest of the exhaust system...
AFM...is common. I am currently using a 2l AFM in my car with no problems...
DO NOT make the common mistake of putting in a 2.5 litre engine, with 2.5 litre injectors but connected to a 3.0 litre ECU. You will run lean...and basically have no power or top end. When the AFM measures the amount of air going in, the ECU will interpret this volume into the equivalent in fuel and times an injection pulse. But it expects to find the bigger 3.0 litre injectors and delivers a pulse. If 2.5 litre injectors are present, for the same pulse width, less fuel is injected...hence, lean. If the difference is too large, the ECU gets confused because your O2 sensors will send back an unacceptable value, and the ECU may interpret it as O2 sensor failure instead of mismatched injectors but will not be able to detect anything electrically wrong with the O2 sensors. If the ECU is unable to resolve this conflict, it probably will go into "limp" mode...a safety mode to preserve the engine until it can be looked at by a mech.
Also, never match a 2.5 litre gearbox with a 3.0 litre gearbox ecu. I don't know for sure, cos I've never had the money to experiment...but I suspect the gearshifts will happen at the wrong times...
Y-pipe becomes mandatory to retain acceptable performance...
