Lionel used two different cans during the Postwar period. the small milk cars: 3462, 3472, and 3482 used metal cans with a magnetic insert.
The large milk car 3662, and Bosco car 3672, used plastic cans with a metal base.
As BANDOB discovered, the cans are not interchangeable.
When the Lionel platform is set up with the track it was designed for, there isn't much space between the platform, and the bottom of the milk car mechanism. When the voltage is set correctly, I don't have a problem with the cans remaining upright.
I wonder whether your car has a bind that is forcing the use of excessive voltage.
