Norm, I do these, BUT here is the caveat. Plenty of standard gauge PS-1 came without flywheels on the Pittman motor. They drive gears on the axle vertically and there is no flywheel.
The PS-2 have a axle based flywheel that is not feasible to add to a PS-1 that doesn't have it. So look at your motor assembly and see if you have a flywheel. If you do they can be upgraded. If not, you need to go with a ERR System that doesn't need flywheel to have cruise. G