According to my best estimate id say 1979. Check on the port side (viewed from behind prop). With the cowling off you should see a yamaha emblem on the casting over the piston or the electrics will be by mitsubishi. I'm pretty sure this is a japanese built mariner made by yamaha. They r great...ive got a 30 the same.
If I'm reading the chart right I figure it is a 1977 - the serial number is 59442 and falls in the range of 664 -26741 to 664-270710 this says it is 1977. Am I reading this right?
Yep that's it
My first guess was just from a quick glance.
Looking properly you are right, 1977 is the year.
You will be able to get parts from yamaha or mercury!!
Any Q's ill try answer; just PM me