Weighty matters

The Earls chassis has been mostly built. The two N-drive chassis has been wired together and a cradle made to hold both together in double Fairlie fashion.
After a spin arround the test track, it's lacking the power to pull 4 carriages (maximum amount it can pull due to size of station platform).
So lead was placed on top untill it would pull 4 carriages, it weighed 150g when it could finally pull 4. So now I need to fill the inside of the engine with lead untill it weighs 150g.
Some people might think it'll be difficult with the amount I need to put in there.... But I have a plan!