Either running or on the wall I have 18 F3 A B units, which I assumed were all Lionel. Tonight I realized that one set, an A + B + five 15" cars in SP Daylight colors (which I've had for about 40 years) was different. "A" has less vents between port holes. The Northern Pacific unit is Lionel.
These were ordered as shells only and fit on Lionel and Williams mechanisms
And the "B" unit has three (3) port holes on each side. No markings inside or out.
Both units have diaphragms. The set was a custom re-paint by The Scale Rail in San Jose CA done in the 70's.
Any one know the source of these units?
Thanks