Check the gear box cover on the trucks. Sometimes they hang low and can hit the points or a high frog.. I have had them hang up on kadee ramps.
A company named C. H. B. models made white metal casting of logging blocks long ago ( 20 years). Maybe they will show up on Goggle.
On the PRR the large "S" was for company SERVICE. Used to carry railroad stores items.
Jameco Electronics www.jameco.com sells robotic parts and componets. Give them a look.