The engine is 25 cubic inches displacement (420 cc), and the 25 cubic inch engines were 11 hp. However you seem to have left out a digit in the first block of numbers (the Model) so that is as far as I can get. It was made on 25 July 1979, as you said, but the 11 on the end of the Code is not the engine's advertised power output, it is the Briggs plant number of the place where it was manufactured. Unfortunately like most of the original Briggs engine plants, that one is closed and gone, so I can't tell you where it was. Briggs now only makes overhead valve engines in the US - the plants that could not get an OHV gig have been closed. All side valve engines are now made in the Chongqing plant.
The most suitable technical manual for your engine is the B&S Service and Repair Instructions 1984, which along with all the others, is available in the engine manuals section of this site.
If you post the full Model number, I should be able to tell you a bit more about your engine.
