I have tried a solution of muriatic acid on the deck pictured below and I did not notice any significant results though I thought what I started with was a bit more defined. However I would not let my experience discourage you from trying .
A friend of mine found the local labs in the SF Bay Area where law enforcement sends a gun when the numbers have been filed off.... they actually x-ray the gun and get good results because the process can image the change in the metallurgy when the numbers were stamped. The lab will also do engine blocks for $400
