I agree with Derek -
"Based on the picture in your other thread I think they'll be fine.
With the floor in place, and the side compartments and front bow cap I think you'll be fine".
plus - with a 9.9 motor, you are not putting a lot of stress on the hull.
now, if you move up to a 25hp motor, more thought should be given to the design.
I run a 25hp (soon to be 35hp) Johnson on my 14' bare bones Crestliner and have never noticed any flex.
These old tins are as tough as tanks !! (figuratively speaking).
good luck in your rebuild !