When I got mine, the seller never could find the numbers either. There was a bit of surface rust that hid them. Once I looked, I pointed and said there they are. He said, wow!, I looked so many times and never noticed.
They are on the left side of the blower housing and vertical. Can be hard to see but ya just gotta get some light in there and make sure the rust isn't hiding them. Right in front of the air cleaner but on the blower housing.