Yep Late 70's to early 80's according to the Briggs engine you have on there.........
The engine has a MODEL TYPE and CODE # on it...... The code number is the date code The first 2 numbers are the year and the 2nd 2 are the month. The other 2 are the day.........
That top pull starter was a very good idea Briggs had...... Most women could start the engine easy..... That's why there was ladies in the commercials way back then............
The engine numbers won't help, since the engine is not original (originals were white). The steel deck mowers came out around 1980, so this mower is older than that. I would think this one is early 70s, since the letters were solid later on.