I'm glad I bought my old spec MkV in 2003 when it was only £250!!
Is the number 27766 stamped? I have a Faz MkII with the electro pencil markings and the original lightly etched number has been over stamped heavily with a completely new number series by the Fins. You can just see the faint outline of a few parts of the original number underneath. The new number on my gun is 77777 which was a nice touch, its also been cleaned up, removing all the weld marks and splatter and then reblued, all part of the Finnish rebuild. If you post a photo t should be pretty easy to confirm it as a ex-Finnish gun, it may even have a SA marking.