On a wild shot, are there any version 2004 interactive flat cars fro the early 1900s period? truss rod would be nice if poss but i was pretty sure they may not exist. any hints or clues ? i looked but there seemed to be only modern ones .... thanks for any help on this.
Have a look at works by 'Pencil42' on the DLS - quite a lot of turn-of-the-century Virginia & Truckee stock in there. I believe the flat wagons are industry enabled, as you requested.
I did a few from that era last year. Industry interactive with custom made products. Made for 2012, but should work for 2004.
Look under Fitz505 or kuid 67794.
Dap has done some nice flatcars too. Janey couplers and air brakes though so they may be a bit later for your purposes. (I just checked and it appears that he used attachment points for the couplers and air hose so it might be possible to replace with link n pin.)
Edit: I just gave it a shot and since DAP used bogie type couplers (as vs. mesh) you don't have much choice on link n pin so far as I can find. tbryson2 has a pair but they were designed for a locomotive. They work but don't look all that good on a freight car. Given wva-usa's comment below I'd stick with the Janney's.
Edit again: Just checked and DAP's Wooden Flatcars use pencil42's Janney couplers which were designed to be compatible with link n pin couplers so feel free to mix them.