That's a beautiful frame! Some SERIOUS bending work on the rail that goes around the motor to the endbell side of the axle tube! If the car ever chatters, that might be where it will be - in that short length of single brass rail under the endbell that might need strengthening.
Here's how I have done the mounting system on some similar cars:
Each brass plate has two M2 (or #2-56) nuts soldered to the ends and the strips are glued to a strip of firm foam rubber, like weather seal or similar, then the foam strips are is glued to the body. This allows a way to accommodate the curvature of the body sides, and makes for a nice flexible system that is very shock resistant.