I wondered about that, too. 

It will take some digging, but I am fairly certain that I saw the BCK cars in the Southern Tier of NYS in the 1970s. 

I have an Erie-Lackawanna equip book, and Group 7 Sheet 21 shows ERIE 86000-86499 built 8/52-11/52 in the Dunmore Shops with Youngstown 7' doors, IDE ends and diagonal panel roofs, Ajax handbrakes, Barber Stabilized Ride Control trucks, but no mention of running board mfr.

The PRR car is class X43B, and I'm fairly certain that the model is correct.

I think Ed's list may be of cars built by car builders, but not the RRs.

Todd Sullivan