Johnno, the first six digits in the third block of numbers are the manufacturing date. Your engine was made on 9 April, 1980. It is an 8 cubic inch displacement (130 cc) and a "first generation" design (the second digit in the first block) with a horizontal crankshaft (surprise, surprise) and a Pulsajet carburetor (third digit in the first block), plain main bearings, and a rewind starter. The Pulsajet carburetor was Briggs' premium small-engine carburetor: it has a built-in fuel pump to lift fuel from the tank under the carburetor, into a small chamber right under the main jet's pickup tube.
Briggs does not have documents for precisely your engine, but here is the owner manual for the closest one they have:
http://bsintek.basco.com/BriggsDocumentDisplay/default.aspx?filename=flivAJX-nfBhU7yand here is the illustrated parts list for the same engine:
http://bsintek.basco.com/BriggsDocumentDisplay/default.aspx?filename=Z6jmyBVJ1DajIIf we can be of more help please let us know.
