That revolver missed the antique classification by only a couple years, but is considered a modern firearm by the BATF. You could contact the BATF and petition to have the serial number replaced on the butt. This happens more often than you think and the bureau has allowed this in the past. If you get a letter from the BATF allowing this to be done, any gunsmith would be able to put a serial number on the butt.

Given the circumstances, age of the gun, and family history, they may allow you to replace the number, problem solved. You can verify the serial number by also looking at the bottom of the top latch and in front the latch in the rear of the top frame. Some call it looking between the "ears" ti see the number. It may be partially stamped on both the left and right of the latch pivot point. Also, the serial number may be found on the back side of the right stock. It could be written on the stock with a pencil or stamped. If all numbers match, make sure you include that information in the letter. If the gun number does not come up stolen, might be able to make it right again and keep it in the family.

__________________
Gary
SWCA 2515