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The serial number has the Model Number to be 7060527 which makes the engine year to be 1977...L = Long Shaft (20 inches), View attachment 22088
http://www.marineengine.com/parts/mariner-outboard-parts/60-2-cyl/675304181-and-up
https://www.boats.net/catalog/mercury/outboard-by-year/mariner-outboard/1977/7060527
https://www.crowleymarine.com/mercury-outboard/624.cfm?q= 7060527