Ray:
The giveaways about how old the F unit is are the 4 wheel drive and the pin on the front coupler.
The Pin was to connect with something else, but I'm not sure what.
Some early N gauge units had a rigid 2 axle frame with pivoting 1 axle trucks, with the truck frames coming back over the rigid drive axles, making the unit a 2-4-2.
I though it was only switchers, but it looks as if the F unit has it too.