Bill
I would have to second Rod's thoughts on this project. This is the perfect time to get the plan together as a foundation to build a trainset on. Even if it is just used for special charters, similar to the way Strasburg Railroad has an entire photo freight train, it would be a worth while endevour. Antoher resource to discuss regarding trucks would be Hamilton/WP&Y. They may be a more cost effective solution even if not exact copies.
As far as adding steel to the cars, I would shy away from that as that would be altering the original construction techniques. Also that may affect several other aspects of the cars integrity. Seeing the fine work the friends do with the freight cars it would be a shame to cheat on the coaches. There are several resources out there detailing wooden car construction. One of the best starting points would be reviewing the techniques discussed in The American Railroad Passenger Car Vol. 1&2 by John H. White Jr. and in Railway Car Construction by William Voss reprinted by Orange Empire Railway Museum. The Stuh museum recently finished the restoration of F&CC # 65 a few years ago and they thoroughly detailed the cars rebuild on their website.
Kevin