Restricted fuel supply would show itself at times of maximum fuel consumption - acceleration and hill climbing - not at low rpm.
Yes you can observe the engine - keep your hands out - as its torque is applied to the motor mounts. Set the parking brake. Idle the engine in N. Observe, shift into D apply the foot brake as well and slowly open the throttle - the engine will move to the side somewhat against its rubber mounts but not too much. Try same in R.
When was the power steering fluid and filter last changed? 1985? There's a small paper filter in the PS reservoir that ought to be changed and the fluid gets like syrup after some years.
Has anyone recently adjusted the rack damper bolt? If so it's too tight.
Throw away that misinformation manual and buy a M-B manual or CD.