Ron Merrick wrote: "Talk about deja vu -- I remember seeing an L&NW "X29" car passing through Kansas on the Rock Island in about 1972, give or take a year, and I got a picture of it. I'd have to look, but I'm pretty sure it was the 5004."
The car number was more likely L&NW 6004 - 58 ex-B&O M-26 subclass boxcars were numbered in the 6000-6057 series. 5004 would put it in the ex-B&M XM-1 SS boxcars series.