You could go through the trouble of having a police crime lab bring the numbers up on the block by stress relieving it.
When a punch is used to stamp numbers in a piece of metal the metal is compressed where the stamp is.
This stresses the metal... there is a process to relieve the stress by heating and quenching with acid or something...
This is how the police find the serial numbers that have been ground off.
It is a one shot deal... so you had better have someone there that can take photos and also notarize the findings.
I have been told that the police will do it for free... as a "learning excersize" for their crime labs.