Acoustic Guitar Construction

My student Michael has been going hither and yon to buy used tools for the shop he is setting up at home. He found this Stanley plane and it is unusual in my experience. It's completely functional, but the blade is certainly not a 'standard' one.
Has anyone seen this type or know anything about it?
It is stamped 'England" and SB 4 or S8 4

Pretty neat plane. Here is what a well known woodworker says: https://paulsellers.com/2013/05/stanley ... sb-4-junk/

If it planes good, use it. You don't have to have fancy tools to get the job done. My two cents.