For many years I've had my eye out for an original tender for the my Erector Hudson (which were originally sold in the 1930's both with and without a tender), and finally located a very nice one at a reasonable price. It came as part of a complete engine-tender-box of extra parts set. Although cosmetically the engine is not as nice as the one I had in my collection (some minor rust on the rods and other plated parts, the smokebox painted black and someone rather crudely painted "Union Pacific" on it), I was pleased to find that the drive elements for the engine were intact. The set box also contained the track, two of the Erector P58 low-voltage motors and also lengths of the "ladder" drive chain. The motor mounting brackets were not there, but this being Erector you can always build things from pieces. Several hours of fitting and tweaking later (including trying different lengths of chain), I got it running. The key to running it on its display track (which is wider than standard gauge by the way) are the pair of "LS" "jacks" that are included; these are basically standoffs that lift only the driving wheels just a bit off the rails. The middle set of drivers is geared off the driveshaft from the motor, the driving rods do the rest.
As seen in the photos, the Erector Hudson is massive; the engine and tender together are about 4 feet long. I put a Lionel "O" gauge 773 Hudson in the photos for scale. Enjoy.