Gents,
The infomration that I have says that work cars 4 (ex-baggage & Mail) and 25 & 26 (ex-coaches) were retired as of 6/30/47. 10 & 11 were retired as of 7/28/43. All of these had been accounted as passenger cars until 8/1/37 when they were moved in the work equipment account.
In 1976 I exchanged letters with Mal Farrell after his book on the WP came out. He provided these numbers of flat cars sold to the US Army [He says sale was 8/30/42]: 76600, 76614, 76617, 76628, 76633, 76640, 76646, 76661, 76668, 76680
Brian Norden