Want to make static display to run tinplate engines

I'd do rollers myself.  If something causes a "shimmed up" engine to shift down onto the rails you're looking at a catastrophe. 

What are these roller sets called ... who sells them ?

Just Google O-Gauge test rollers.  There are several sources.

I made some test rollers myself didn't cost much.I used bearings from those spinners that you see in stores now.Using shoulder screws and some shims mounted on angle aluminum.Only cost me around 20.00.You have to measure better then  did but I only use them to test motors when I rebuild them.I just attach jumpers to get power but you can add a rail between the aluminum.

You should really used sealed bearing for this application.  I have a set of four from micromark but there are others out there.

Depends on how fancy you want to get. This is my adjustable roller base, which can fit most engines. There were a few threads on here about building these a couple of years ago. 

That's looks really nice.Like you said depends how fancy you want to get.Made mine just to test things I can see everything going on .Maybe one day I'll do something like yours.