Trains did a nice overview of this subject a few years ago in the December 2010 issue.
Active:
-972551 (Alco 1925; NP heritage; stationed as of 2010 in Dilworth, Minn.)
-972552 (Alco 1907; GN heritage; stationed as of 2010 in Glendive, Mont.)
-972554 (Alco 1937; NP heritage; stationed as of 2010 in Glendive, Mont.)
-972555 (Alco 1925; GN heritage; stationed as of 2010 in Glendive, Mont.)
-972558 (Alco 1915; CB&Q heritage mated with RSPU 972573 which is ex BN F9B 775; stationed as of 2010 in Lincoln, Neb.)
-972559 (Alco 1915; NP heritage mated with RSPU 972572 which is ex BN F9B 769; stationed as of 2010 in Alliance, Neb.)
-972560 (William Bros. 1950, NP heritage; stationed as of 2010 in Grand Forks, ND.)
-972561 (Alco 1927; GN heritage mated with RSPU 972577 which is ex BN F9B 777; stationed as of 2010 in Wenatchee, Wash.)
Stored were rotary 199361 which is ex Santa Fe along with RSPU’s 972570 (BN F9A 784), 972571 (F9A 812), and 972575 (F9B 833).
I suspect all these F9’s are of NP heritage. I think the Burlington’s rebuilt F7 that was turned into a F9 was gone by merger (They only inherited 1 CB&Q F unit as I recall and I think it was a F7), but I assume that Great Northern’s 6 B units (They didn’t own any A units for this model) made it to the Burlington Northern roster so it’s possible I suppose. But there were over 30 NP F9B’s so it’s unlikely.
And since this time, the 972554 has been rebuilt by Relco with an entirely different carbody and it seems to now have a self contained power unit to power the blade. Relco has also rebuilt a few of these in-kind. And someone sent a F unit to Relco for rebuilding a year or two ago but I forget if it was BNSF or one of UP’s ex SP units (I’m leaning towards thinking it was a SP unit… Trains carried a picture of the move a while back). And the 972551 lost her blades in 2011 due to failure but has