As you can see, there is a lot of diecast decoration preventing access to the wheels. Releasing the 2 screws lets the wheels on the opposite end become accessible, but it is the red wires for the center rail contactor/rollers that prevent the tires wheels to move much. I took the cab off, but the wiring is such a mess inside, I decided against that approach, which would have involved unsoldering the wires. I thought about cutting some of the diecast material away, but rejected that also. Eventually I did get the tires on. I have an upper level in the layout, which the engine could not climb up to, now it can. 
The tires were removed earlier because the engine would stall going across switches. It needed those 2 wheels to get the ground. I have since added a wire between the two units so that is less likely to happen.
