I am seeing the following numbers:
Floor plate - 2661
Underside of barrel - 3673
Handguard - 5973
Bolt - 1408
Under butt plate - 1456 with a possible "O" prefix or suffix
I do not believe any of the numbers, with the possible exception of the number under the butt plate, is a serial number. They may be assembly or lot numbers.
The serial numbers on sporting rifles and civilian Mk II** rifles are numeric, and are on the left side of the barrel and under the butt plate. I also have a civilian Mk II** butt plate that is serially numbered on the inside. I do not know how civilian versions of military rifles were numbered. According to TRRS, military rifles were serially numbered 1 to 1,000 prefixed by a letter or letters. Mk II rifles were issued in series A to Z and AA to CR. The information was stamped on the right side of the butt and consisted of the Ross logo, the mark, pattern, serial number and series and year of manufacture. Based on the above, one can surmise there would not be a serial number higher than 1,000 on a military Ross. That being the case, it is unlikely the number stamped under the butt plate would be a serial number, unless it followed a civilian numbering system. If it did follow the civilian numbering system, I would expect to also see the serial number on the barrel.
All of the above likely contributes little to the discussion. Perhaps a more knowledgeable member will step in.