Two problems with this idea. First, something that size makes a really big target. Your mechas would be munitions magnets. Second, the necessary propulsion mechanisms would be very large and complicated and prone to break down; they would be a maintenance nightmare. The mechas would be like early tanks; more in the shop than in the battle.
We could field mechas today if we wanted; we have the technology. We don't because our existing equipment is better. Tanks are lower, therefore harder to hit and easier to protect, and nearly as mobile. Helicopters can go anywhere a mecha can, are much faster, and are harder to hit. Mechas might look cool, but in practice other vehicles are better.
That said it should be possible to create a steam powered steel limbed walking machine with late nineteenth century technology; making it practical is a different matter.