;D
Open it up and see how much space you have.
Get some tungsten from Hobby Lobby. It comes in putty form also.
Rich
Jack,
Balance can be just as important as weight. If you've added weight to the cab, you should balance that with added weight towards the front, so the center of gravity lies between the drivers. Usually there is a bit of dead space in the very front of the smokebox. Also, I have added a bit of weight into the stack, painted black so to hide it.
I like to shape fishing sinkers. They are soft and can be shaped with pliers or a small hammer.
Regards,
Jonathan