While it is not strictly necessary, it is easier if you remove the blower housing.
Then remove the power feed to the starter.
After that it is just 2 bolts
One is easy to access, the other hides partially behind the starter pinion.
Both have a torx hole in the middle, some thing around a # 40 from memory ( probably wrong )
However if you rotate the starter pinion to the top so it engages with the flywheel there is space for a 3/8 drive socket head to get in or a 1/2" drive long reach.
You can use a ring spannar but you only get about 1/12th turn at a time unless you have a cresent ( banana to some ) spannar .
It should be a dead simple job & B & S should have changed that mounting 40 years ago. the bolt just has to move 1/4" out.
One of the reasons why I hate working on B & S engines let alone the 3 spanners two screwdrivers and torx driver needed to remove the blower housing to start with plus pliers for the fuel pump hoses .