Another approach I've seen for large-scale models of a similar size is to recreate the motor mount of a full-size trolley, with nose-hung traction motors (sized to fit between the wheelsets parallel to the axle) engaging a 'bull gear' on the axle. One end of the motor mount sits on the wheelset axle (in the photo I found, brass strip was wrapped around the motor and the outer end shaped to cup atop the axle), the other end hooks over the truck bolster. Of course with a single-truck streetcar this half of the mounting would be on some sort of frame extension.
