This frame will hold the motor, circuit board and trucks from a Rokuhan Shorty "Chassis B" locomotive. It was specifcially designed to fit the H10-44 shell produced by Walt's Trainz and Things sold here on Shapeways.
Visit his shop to get the shell:
https://www.shapeways.com/product/BETYEMMSM/fm-h10-44-z-scale?optionId=60956321&li=marketplace