I flew both planes, the 727 and the DC8, as engineer and co-pilot and finally the 727 as captain.
The 8 was a piece of work. It was a nice plane to fly but heavy on the controls. The plane lagged far behind the control inputs. On the approach you have to be absolutley stabilized inside the outer marker or it was ugly trying to correct as most new pilots aleays over corrected.
As being an engineer on the 8 I disliked having fuel the airplane. You need to remain with the plane and manually open and close the fill valves to balance the fuel load. The 727's fueling valves can be operated by the fueler at the fueling panel. It was easy to flame out an engine if you forgot you were transfering fuel. No I never did it, but I know two people who have. It's not uncommon.
The 727 is, from my experience and the testimony of pilots who have flown other planes, the sweetest airliner to fly. I can only compare it to the DC8. Down low when being vectored for the approach is when the 727 is a joy to fly. Very manouverable. The plane is very responsive to control inputs. Literally if you can fly a cessna or a piper you can fly this airplane. It's that easy.
The engineer position is great. I know I spent 99 percent of my time as an engineer with my seat facing foward nudged up to the pedestal. It was a phenominal experience. I loved being an engineer. Being an engineer allowed me to transition into the right seat of the DC8 with 350 hours TT. I couldn't have done it unless I occupied the engineer seat first. It taught me to fly the plane. By the time I had upgraded I knew all the profiles, and numbers for the plane. Ie. airspeed and power settings.
Yes it is the F/E's job to hold things together in an emergency. The reading of an emergency checklist is an art. You have a rythm or you don't. It is a action response checklist. The engineer reads the checklist item and it's appropriate action and then the appropriate crew member will complete the action and then recall the response. It is the engineers job to verify the correct actions are carried out with the correct response. But when things get tough in an emergency a good engineer knows how and when to complete the checklist himself.
There are only five items in the 727 cockpit that need verification of another crewmember to move. These items are the fire handle, the thrust lever, the start levers, the fuel shutoff valves, and the CSD disconnect. Everything else can be accomplished without the other crewmembers verification. A good engineer knows when it is time to accomplish a checklist by himself.
The only thing I hated about the 727 as an engineer was that the space was a little cramped. It was hard to turn your seat from the side facing position to the front without brushing your knees against the sharp bolts holding the armrest on to the first officers seat. I removed a fair amount of skin over the years doing this. Also if the FO put his seat back as far as it would go the engineer would have a cranium on his desk.