I believe a printed wheel will be fine. I wouldn’t even consider a plastic tire. We had the wheels printed and will have the tires milled from regular mild steel. Now we had talked metal centers but we are going with all plastic. we will see how that works.
Of course shapeways has two forms of metal 3d printing. One uses an ink jet style printer to squirter glue into stainless steel powder which is then baked to fuse it then it is saturated in Bronze to make a strong structural part. They also print wax patterns that are then used to make investment castings from several choices of metal. These both make good detailed parts that are strong and heat resistant (I do live steam) the stainless/bronze method can be hard to machine well but the investment castings should be fine.
There are several wheel suppliers in the UK - in particular Slaters supplies nylon wheels with steel tires (tyres), and Walsall sells cast iron wheels ready for you to machine. Unfortunately they are mostly standard gauge types (lots of spokes) and they aren’t cheap either!
Interesting pics. I wonder what the story was on that “kitbashed” gon?
Railroad builders give discounts for recycled parts. Those gons were probably going to haul scrap iron, didn’t have to be pretty.
Those pics came from Pennsylvania Steel country.
John