What size do you or anyone, think the width of the chain used on the wheels, is?
I have some Servo-link chain and sockets and the chain is 1/8" wide. I bought the stuff about 6 years ago to build an Ollie Smith (NZ) Railtruck that used chain and wheels sort of like shown in this picture. I could never figure out the width of the chain so I never built the model.
Looking at the proportions of the driver's body, the railhead & general mechanicals I would guess 2.25" to 2.75" wide but parallax error in photos can be very misleading, especially partly angled photos such as this one.