Hi David, must admit I'd have put the motor in the other way around with the bulk of it in the cab bunker. So long as it is below the level of the cab doors so that there is daylight through the top a strategically placed crew would hide it. A number of my locos have the crew, often with lumps of lower limb and torso removed, attached to the motor and nobody ever spots it. The great advantage of this is that the motor is very light, keeping it toward the rear means that the tanks and most of the boiler, which sit over the drivers, can be stuffed full of lead or preferably copper tungsten. The more weight you can get over the drivers the better in 2mm for traction but particularly pickup.
Regarding the 30:1 ratio, combined with nigelLawton motor it will require a gentle hand on the throttle but will be perfectly controllable. If DCC, a CT chip would give good results.
Jerry