My Sea king section stops at 1980.If you tell us the hp it will be easier.
I believe the prop is a spline drive so the pin is a "prop pin" used to position the prop.
Take the prop to the hardware store and select a brass or stainless pin you may have to trim the length.
A Chrysler guy may be around with more specific info.
1. You can make your own. Some were made of brass and others of stainless. Obviously brass would provide more protection. Take a set of drill bits and play with them till you find one that just barely slides through the hole in your prop shaft. Length is the length of the slot in your prop hub. If you can't find brass rod anywhere, get online and look for it. One place that may have it would be a Scott Attwater site. We used to have a Scott, back in the -50's vintage, and at the end of the steering arm was a factory installed rubber grommet that held 2 pins and two cotter pins. One of the old sites may have a collector that has pins in stock and giving them your dimensions may get you what you want.
2. All of my life, until I joined this site, the pin was referred to as a "shear" pin as you noted. We called them shear pins because that's what they did. Getting on here I find that the proper name is "drive" pins. Learn something new every day. But my experience was that they sheared when you needed them most and didn't drive.
Looks like your outboard is a 1982 model year 15 hp? You can still get the shear pins from any Mercury/Quicksilver parts dealer. Part# is FA324101, you get 3 pins (and a fresh cotter pin for the prop nut) for about 10 bucks.
