[HamiltonJay]

You are correct, but the main thing with the 320 retrofit vs the 737 is that the 320 was far enough off the ground to keep the engine under the wing... Yes it needed work.. but it still remained under the wing.

It wasn’t hey, strap that new engine on with no other work, didn’t mean to imply that’s all it was... It was indeed work for the 320 to get those more fuel efficient engines on it.

[RayChuang88]

Actually, another thing adopted as standard on the A320neo Family was "sharklets"--i.e. large winglets--as standard on the wing tips. But the wing is still different than older A320 Family models due to the need to accommodate the large fan PW1100G and LEAP-1A engines.

Indeed, the A321neo Hawaiian Airlines now operates has the range to fly from the US West Coast to Hawaii easily.