Better watch it with collecting Marx scale tin. I started down the road to the "tinplate side" that way. Now it has spread to Marx 6" and 7" tin, prewar American Flyer and Lionel tin, and lately even Hafner postwar tin.
Oh, by the way, Marx 7" is very similar to the Marx 3/16" scale stuff. If you want more diversity in your trains, converting the 7" to 8 wheel with scale trucks is a simple conversion.