I have picked up a very cheap toy coach that may prove useful on the FCPyF. It’s a 1970s vintage Faller “Hit Train” vehicle, roughly O scale on 32mm gauge wheelsets. The Faller website describes the trains as slightly smaller than most O scale models but they’re supposed to be standard gauge vehicles and narrow gauge trains are generally smaller anyway.
Photo – eBay vendor.
Obviously the running gear and couplings will require changing before the coach can be run on the Pampas and Fernandez but it should go well with the Fleischmann four wheeled coach and shortened Lima GW brake (now running on a six wheeled chassis) to create a local passenger train for the Grande to Cuarto service.
If the coach does make a suitable On30 conversion I’ll see about getting one or two more to strengthen the Cuarto set. While looking at the Faller products I noticed a diesel loco that might also be a candidate for conversion.
These seem to be a lot less common than the coaches though so if one does turn up on eBay the price may be prohibitive.