Thanks to Pingman's mid-January post (since deleted -- TOS issues??), I ordered a set of Micromark rollers (then on sale). I ordered the O-gauge set of rollers with the idea that I'd have pull them apart and set them up for my S-gauge engines. For those interested, here are some pictures of my new test stand based on the re-gauged rollers. Here's the rollers as received and with the plastic spacer plate removed:
One of the advantages of being a woodworker who can never throw "good" pieces of wood away is you can always rummage around and find what you need without making a trip to the lumber yard. So firing up the radial arm saw and my router table, I cut up some prefinished baltic birch plywood into the necessary parts, borrowing liberally from ideas posted here by Laidoffsick and others. The base is 26 inches long by 4 inches wide with a poplar runner, sanded smooth, on which the roller and track stands can slide.
I remounted the rollers on the plywood stands - the wooden spacer was ripped to the right width to serve as a locating edge to give the right distance between the rollers (7/8" is the inside-rail to inside-rail distance for S gauge).
Before assembling the stands, I counterbored a hole to mount the T-nuts for the 10-24 thumb screws that I have had floating around in my collection forever. I wasn't sure I would need them to lock the stands in place (turns out they slide on the runner pretty easily), but the T-nuts could not be easily added after the fact.
The complete test stand has a 13 inch section with track for the tender and trailing trucks and a 3 inch section for the pilot (again based on what others have posted on OGR). Both track sections also slide along the runner, and just to be 'safe' I also put a T-nut on each, though they slide with some resistance.
Finally, in use with steam and diesel locos