They sell a kit. It comes with wheels, axles, spacers, and directions. You may need their puller. All I did with the ends was screw the bottom steps on permanently. Made me happy, but it would probably drive the 3-rail scale crowd nuts. I know they have incredible heartburn with handrails that stop too high on the ends.
I did machine some brass coupler pockets - a very big deal made simple with an end mill. Wood shims would do fine.