Thanks archangelski ..
I know there is a corridor, but can another person sit beside the pilot?
Not really.
The pilot’s cockpit and rear crew cabin are connected by a small gangway featuring some stowage racks on the right side, holding electronic equipment.
Because no bulkhead is installed, pilot seat rear is accessible. Flight engineer usually sit in aft cabin. When needed, he can walk through the “corridor” to access electronic racks or pilot seat rear.
If needed, I have other pictures of this gangway, with pilot seat clearly visible (and the available space for crewmember to get his head).