Just replaced engine coupler, still need to replace gimbal bearing. Should I install the bearing or the motor first?

Either way, the bearing has to be Installed in order to check engine alignment to the bearing and adjust accordingly

That said, if you install the engine with the old bearing and the bar goes right in to the coupler - when you install the new bearing, it's only the gimbal that needs alignment to the engine, not trying to see which (engine or gimbal) needs to be moved for proper alignment