I worked on a 1959 Sea King 12 HP which belongs to a friend. I replaced the water pump impeller, cleaned up the carburetor, cleaned the prop up, and replaced the lower unit oil.
Manuals:
https://www.fiberglassics.com/wiki/images/b/be/Johnsonservice001.pdf
https://www.marineengine.com/parts/vintage-evinrude-johnson/376747/catalog.html?https://www.marineengine.com/parts/vintage-evinrude-johnson/376747/37674700001.htm
(lower unit exploded view is better on the second link)
Impeller is Evinrude part number: 775518
https://www.marineengine.com/newparts/part_details.php?pnum=OMC0775518&ptype=&Engine=&Model=
Carburetor Kit: 439071
https://www.marineengine.com/newparts/part_details.php?pnum=OMC0439071&ptype=&Engine=&Model=
Manuals:
https://www.fiberglassics.com/wiki/images/b/be/Johnsonservice001.pdf
https://www.marineengine.com/parts/vintage-evinrude-johnson/376747/catalog.html?https://www.marineengine.com/parts/vintage-evinrude-johnson/376747/37674700001.htm
(lower unit exploded view is better on the second link)
Impeller is Evinrude part number: 775518
https://www.marineengine.com/newparts/part_details.php?pnum=OMC0775518&ptype=&Engine=&Model=
Carburetor Kit: 439071
https://www.marineengine.com/newparts/part_details.php?pnum=OMC0439071&ptype=&Engine=&Model=