Old Guy!
Just seeing this thread now and i agree with your assessment- that looks like a Prospector Fort model. While your dimensions are a good indication, as Andre notes, Chestnut specifications are more of a rough guideline than an actual certainty. Better yet is to examine the ribs: the ribs in my Prospector are considerably beefier -wider and thicker- than in my Pleasure model Pal. I do note that this specification seems to have changed in the later years- my Pal dates from 60's, my Prospector 1970...
And while comparing your canoe to Bill Mason's is useful keep in mind that they are generations apart in age!
Yup, they are great fun to paddle- enjoy your Prospector.
Bruce