Answers from the Past !
First for Ben, The top of the line cleaner (SC688) had the the First Generation
VG I in it because it was made of Stainless Steel ( not Chrome covered Alumin ). The Helicol (SP) Steel, like an air plane propeller. With Sealed Steel Ball Bearings.
Which always gave the best service and easy brush replacement in the High use Commercial Business. So the V G II may have been the Newest Roller in the line up. It was not the greatest, as they only had "bushings" or "Sleeve" bearing. Which over heated and worpped the Plastic Casting base of the cleaner. I actually saw Cleaners that had V G II in them with holes almost poked from the inside out.
So in those early 80's. They only used VG II with 3.5 Amp. motors with top and bottom ball bearings and the small
(Blender) motors. As they had a lower rate of RPM's.
Now the SC 679, Maid saver did have a Beater Bar Brush Roll. It was the wooden
roller, with the red plastic beater bar, with a single brush strip on the opposite side. The vacuum did have the "blender" motor, with the small armature and the Top Sleeve Bearing motor.
I would say (but do not remember for sure) that the SC684 had a 3.5 amp motor.
The SC 886 & SC 888 had a 6.5 amp. Now not sure if the SC 886, could have had one of the first VG II with sealed bearing ??
Hope that helps bring things into focus.
Norm