[njsteve]

The process used by law enforcement uses heat and an etching formula that allows the image of the prexisting numbers to appear for a very short time. The combination of heat + acid molecularly destresses the pounded-in portion of the metal and allows to it raise just long enough for a photo to be taken. The photos are then used as the evidence because the engine pad then reverts back to a destressed condition and the numbers are then lost forever. (Sounds like something out of Raiders of the Lost Ark). It's an magical process to watch, something on the level of alchemy. If you have a local state police or county crime lab in your area you might want to give them a call. Most of the older guys in law enforcement I know, have an affection for old musclecars, and might be happy to assist you. Plus, it gives them practice in this tricky procedure, in a way that won't jeopardize a case if it doesn't work out well. -NJSteve