3 orders of them (click for spec sheets)
1923 - Worthington Feedwater heaters, small tender
1926 - Elesco FWH, long haul tenders
1928 - Elesco FWH, medium tenders (except 1409 as built which had a Coffin FWH, later converted to have Elesco)
First two orders included locomotives for SOU and subsidiaries, CNO&TP and AGS. The last one for Southern only. The CNO&TP locomotives were equipped with Wimble smoke ducts.
I've got a complete set of erecting cards and details for every little thing on the Ps-4's.
The 1928 orders came with Walschaerts Valve gear, the previous orders had Baker and most were rebuild to have Walschaerts.
All divisions were given freedom for modifications, practical and cosmetic. Bunker extensions, cab rebuilds, and tender swaps all were very common. CNO&TP locomotives, as well as 1401, were given the unique number plates. Many locomotives were decorated with brass eagles and candlesticks and adorned their assigned engineers' names. CNO&TP 6482 "Queen Bee" had nearly all this added. Engineers were also given freedom to use the whistle of their choice, be it the standard 3 chime step top, or the famed 3 chime long bell, or even a personal whistle.
Famed rail designer Otto Kuhler, in 1941, streamlined the 1380 for use on the Tennessean between Washington DC and Monroe, VA, the handover point for the N&W section of the route. N&W had a no diesel policy, and Southern did not want to tie up its new diesels on such a short section. It was said to be his favorite locomotive that he streamlined, and it is rumored that he was never paid for the work.