If it's O gauge, wooden bits can be made of close-grained wood. In this case I've used (I think) basswood, or as we call it, lime.
At 1mm thick, it's easy to work with a sharp knife, being careful when cutting across the grain. A light sand and the bits are ready to superglue in place. The only tricky one was the backs for the middle seats. After much faffing, I glued one end in place and then pushed the other where it should be (the wood fits between the poles) before the glue fully set and still had a little flexibility.
The lengths of balsa signify that the wooden bogie's guage has been reduced to 21mm for the 3ft track that I don't own. I've a few ideas about this but they can wait for a bit.