As far as I know there is only one place where you'll find this and that is the one located on the frame rail under the seat. I also have a 1961 and sandblasted the frame myself and don't remember seeing any other places being stamped. Here's what the Complete Corvette Restoration & Technical Guide says, "The serial number on 1956-57' Corvettes was located on top of the outside frame rail, at approximately the driver's hip pocket. Usually it lined up with the "X" section in the frame center, and could appear on the inner or outer half of the outer frame rail. Ther serial number was stamped into the frame quite heavily, so a depression around it is evident. The number can be read by standing on the drivers's side of the frame, looking across towards the passanger side." Some frames were stamped twice and I have seen this because my 1961 was one of them. I really haven't found any information in my Restoration manual of them being stamped in any other place, but that doesn't mean it didn't happend because the double stamping thing isn't even documented, but 25% of production from 1954 to 1962 has it. If I find my chassis restoration guide I will try to look it up and see what they say, but I don't think you are going to find that the frame is stamped in another place.
