The one I'm thinking was just the last couple of years, but may have been a sidebar to an article on someone's layout, rather than being a separate 'how to' article...maybe in one of the MR special issues (Great Model Railroads, Model Railroad Planning, etc.)?
Many many years ago like 1957 - 1959 MR ran a 2 or 3 part article on how to make one. As I recall it wasn't all that complicated but like everything else it takes time.
Heljan made a transfer table maybe 15 years ago, but from what I could find it was pretty similar to the Walthers one. Heljan has in the past made products sold under the Walthers name, so it could actually be the same transfer table. I don't know of any other ones; I think one of the train mags had an article on building your own from scratch in the last few years?
(BTW for anyone who's wondering, "M track" is Marklin HO track designed for three-rail AC. The track has a series of studs sticking up in the middle of the ties, and the engines have a long metal slider on the bottom to pick up power from the studs.)
New rookie here. Does anybody make/sell current or in the past motorized transfer tables in HO and O gauge like the Marklin 72941 HO Transfer Table w/M Track Connections but not sunk in like Walthers Cornerstone 933-2968?