The main countershaft installed. The countershaft is put in with new thrust washers and end-play tolerance is measured. If it's ok, the countershaft is pushed out with the dummy shaft and the gear cluster is left in the bottom of the case until after the input shaft is installed. Keeping the thrust washers in place during the rest of assembly is a bit of a trick. By not moving the case around too much, they didn't fall too far out of position and could be realigned with fingers through the ends of the case when needed.