MarineEngine.com does not offer troubleshooting assistance or repair advice by email or by telephone.
You are invited to join our public Boat Repair Forum to seek assistance from other members.
You may also visit the Boat Motor Manuals section of our site to obtain a service manual.
One last attempt to help.----Your choke flappers are working very well.-----You have to trouble shoot why it won't start up after 2 seconds of cranking !!-----That motor when new started instantly so to speak !!----Blunt statement here.-----" It is not uncommon for a novice to jump all over the carburetors when they are in fact NOT the problem"

Only use a factory replacement key.----Make sure tapers are matched.----Assemble with tapers clean and dry !
I can not see your motor !----All I can tell you is how it should be.----The bolts that go through the transom hold the brackets on.----The motor itself is not held on to the boat with any bolts that go through the transom.------But on 50 year old motor with possibly 6 or more owners there are some creative things done .