Easy to understand and proven.
Build wooden outboard motor stand.
Lay the two 36 inch 2x4s on edge on a table or workbench parallel to each other and approximately 24 inches.
Place a longer section of 2 4 underneath the aft end of the stand and position it between the base and the motor board.
Adjust the sides and ends of the base using a carpenter s square so the base is square and drive an additional.
Cut to these lines.
Using the base and the upright support as guides mark the lines on this piece of 2 4.
This will be the aft support of the motor board assembly so arrange it for maximum support of the motor board.