Good advice from Dave. If one is going to invest the time and money to modify 5' gauge O scale models to P48 4'8 1/2" fine scale I recommend you start the best running mech you can find. 3 rail China drive mechanisms may be robust but IMO they fall short of single horizontal motor drives for most models, and especially so for fine sale P48 modelling.
- compromised appearance as the motor(s) intrude into diesel cabs
- due to vertical clearance issues, smallish (low torque) motors are used - impacts starting performance
- again due to height restrictions - flywheel mass is less than what is possible with a single motor horizontal drive train
- generally high gear ratios - again impacting low speed starting performance
- exposed spur gears which over time can pick up layout crud,
- spur gears generally run noisier than enclosed axel gearbox worm drives
- harder to customize (up grading motors, gear ratios, flywheels, ball bearings, etc)
- cannot spring/equalize the axels as they are rigid in the truck block
- and from a P48 perspective - difficult to narrow the back to back wheel gauge due to the die cast block and spur gears
