I bought a Corgi birney to compare with my Lionel ones. I very much like the detail and scale proportions, so thought I would try to motorize it. The method I used turned out to be so simple I thought I would share it. I used the drive from a Williams pump-action handcar, a self-contained unit that mounts under the floor and requires no wiring. You unscrew the truck from the Corgi and also the bottom piece. Then, you attach the drive with four #6 sheet metal screws. You don't want to over-tighten the screws or you will mash the drive gears, just tighten enough to hold the drive in place. I drilled pilot holes into the floor of the Corgi; the screws line up behind the seats and barely show on the interior. I cut out the brakes and springs from the plastic piece, trimmed the ends a little to clear the wheels, and attached to the sideframes, then used a 1/4" shim to cement the sideframes to the drive. The wheelbase is very close, to within about 1/16", and the car rides low (for 3-rail).
Downsides: 1) only runs forward, so you need a loop, and 2) paid $80 for the handcar, so not cheap, but then cheaper than most aftermarket drives.
One thing I wish were different on the Corgi: the finish is very glossy, and
I would like to tone it down without fogging the windows. Any suggestions?
Bruce