I think the correct term is - there isn't enough room to swing a servo arm - let alone a cat!
3" x 4" is bigger than the loco! It's only 120mm long and 60mm wide.
I've tried the Lrp ESC with reverse in the loco and it works reasoanbly well! Just barely skims the rails and misses shorting itself out against the motor by 0.5 - 1mm! The main problem with it is the fact that the motor and battery wires are quite hefty and there's barely room under the chassis for a nats danglies!
I'll post some photos after I've replaced a few screws with countersunk machine screws and cut them to length! Then I might actualy be able to fit the cab onto the chassis.
My next loco model will be a little larger for practicality sake!