On this boat, the flotation in the upper gunwales is only about 1" thick, 4" wide by about 10' long, the blocks down below the side trays are about 3x5" thick and about 5' long toward the rear. The block in the bow is about a foot thick and cut to fit the V shape of the hull, above the floor, but below the seat top. This piece I would think would be the primary piece of flotation. The strips in the floor are layered, it looks like a combination of three strips down each side at the stern, a 3x5" strip, a 1x4" strip, and a 1"x2" strip stacked outboard of the stringers.
If I were to take a guess, and considering this having a 300 lb outboard on the back, I'd guess that it would float bow up in the water, and likely capsize with the motor, fuel tank, and battery likely being in the rear of the boat to weigh it down.
At best you would have a bow tip to cling to in the water. I doubt the amount of foam in the rear of the boat would offset the motor and related weight. This is the earliest 'SS' model I've owned, all of my other boats had only below deck flotation, there was nothing above the deck at all. Those were later models. Maybe they learned something as time went on? Or did they just go light on the foam and its placement to give us more storage compartment space?
The area that's stuffed with foam up front on this boat was open storage space and padded seating on my later model boats.
I'm sure the seat cushions were also part of the flotation but they were only secured by a few snaps, if they would float, they would likely be for passengers to grab onto not to float the hull.
My biggest concern with a boat like this would be to keep it off the bottom if did sink to reduce recovery costs, most of the places I boat aren't super deep or wide, if my boat was sinking, I'd likely beach it first. I couldn't imagine the cost of recovering a boat from the bottom of the river channel or bay. I worked for a company who did recovery work, they weren't cheap and some of the bills for simple little jobs were astronomical.
If a boat isn't 100%, it don't go in the water. Period. But along the same lines, if it cost more in foam than the boat is worth or can be replaced with, I'll find another project.
I have 3 other boats, this one just happened to come along for cheap. I don't want to dump a ton of cash into it, I'd probably feel differently if it were an 18' model.
Right now its got a few inches of snow all over it from last night, I'll do some more exploring and maybe ripping apart when the weather warms up a bit again.