S&W would retain the original serial number if the owner wanted that (most did not). From the photo, it appears the entire revolver was replaced with a new one and the old serial number retained. I assume there is no serial number stamped in the ejector rod shroud or on the rear surface (outer edge) of the cylinder.
The records should show two shipping dates for this serial number. One in 56/57 and one in the 70s. If you letter the revolver and explain everything about your 29-2 to Mr. Jinks in detail with photos, it might result in a very interesting factory letter.
The assembly number for your 29-2, 67258, dates it to late 1973.
Bill