The needle bearings should slide easily with no obstructions. And don't forget the circlips as you go. Remember the input shaft we set aside earlier? You will need to replace the bearing on the end of the input shaft. Use a bearing puller for removal and then press the new bearing into its place. Then slide the input shaft back onto the main shaft over the new needle bearing. As you carefully place the main/input shaft back into place, be sure to notice the circlips on the main bearings. These ride in a slot that will keep the bearing race from moving after assembly. Make sure everything rotates smoothly. Bolt the upper case back into place and torque to factory specs. Put the idle gear/ reverse gear shaft back into place.