Used Mashima motor with mounting plate and worm. This size of motor would suit a larger shunting or trip working 4mm loco, possibly large 009.
Bachmann LNER/BR Peppercorn A1 4-6-2 DCC Ready Loco Chassis With Mashima Motor
Victorian Railway RT rail tractor H0, etched brass kit + BlackBug Mashima motor
Hornby X7886 Class 43 125 HST Motor Bogie With Frame