As one who grew up with a 1959 Flagship, plywood, I can honestly tell you that:
a) Find the soft spot
b) Get out your pocket knife
c) Repeatedly stab her in concentric circles until the knife no longer goes in.
d) Cut six or eight inches of the good wood out too, or until the next frame/rib for fastening purposes.
You certainly do NOT need to strip to determine if there is rot!
The one thing about ply is that you do NOT need to be a master woodworker to repair your own hullsides or bottom.
Be sure and check the frames when exposed. They probably will not be cracked/brokern, however, they may have spots of rot.
Owens were not heavily built boats ... even lighter than Chris Crafts plywoods of the same era.
Qualified survey FIRST and foremost!
Outdrive? This boat should be a straight inboard ...
Nothing else matters but how I raise my children ... and their opinion of me, as a father.