Welcome to iBoats!
Nice runabout!! Sorry, but wet foam will not dry out. Must be removed. These boats are Easy to work on. You won't regret it once it's done. The first link in my signature below has some drawings and info on what you will be doing.
This is a picture of my 1968 Larson All American. I removed the old floor but left a two inches of the old fiberglass around the edges.This way I used the edge as a guide for the new floor.