Crocodiles anatomy is rather primitive: their limbs protrude out of their bodies almost parallel to the ground. This is due to the articulation of the limb with the pelvis/shoulder. 

To have a bipedal posture like birds one has to have limbs getting perpendicular to the ground. With a limited mobility in the shoulder, is also more difficult to move the wings.

So, I think there is no escape from the path of first improving shoulder/pelvis joints to allow bipedal posture. Convergent evolution would give birds roughly the same appearance.