Remove shift cable at the motor.-----Find the hitch pin on that horizontal shaft below the carburetors.----Remove that hitch pin.------Push that horizontal shaft to the port side and rotate it.----Shift rod is now loose.
When choke plate is closed a very low pressure develops in the carburetor when you pull the rope.----Then the atmospheric pressure in the float bowl floods the carburetor throat with fuel.
I have worked on lots of motors.-----That amount of rust indicates water / moisture was in there.-----How it got in there and over how many years is hard to tell.
Those wee handy pumps come with a 3/8-NC thread.-----Very handy to pump oil into the lower unit.----That would be the most common one on the boat shop shelf.-----Not hard to find.
They had a production run of X number of motors.-----Sold the same motor for a number of years.----Then a new production run.------Not much different than what others did over the years.
50 parts gasoline for 1 part oil.-----Seller likely is flipping the motor if he does not know ratio.----Or if he has been running it then did he do damage ?
Turn key to on.----Push in and listen for a click.----Use an assistant to push in key.-----Use screwdriver on enricher and near your ears to listen for " action "