Ike: Yes, the BN was probably the last stronghold for mainline F units in the us. They were still running in 1978 when we moved to Kentucky, often in sets of seven or eight, through Pasco. Surprisingly, the BN green looked good on F units, and with the light rail on many of the eastern Washington branches, they were still pulling 40 ft boxcars of grain. It wasn't unusual to see trains that, at first glance, could have been from the 50s. After we moved, everything changed quickly, but I wasn't there to see it.
The oddest consist I ever saw was A-B-C415-B-A, all in BN green. The Alco on either end wouldn't have looked odd, as most of the SP&S's second generation Alcos lasted through the 70s as well, but in the middle?