I like screw tab in the back but then that means you can’t use a long screwdriver to tighten/loosen.
You are correct.
The pin in the front is ideal.
With it in the back and force on the leading edge ( weird wave chop, kelp, etc…) is a force that can bump it out of the box.
All that I’ve seen locked in pretty tight and would most likely be ok with a pin in the back but if it were my fin I’d move the pin (if you can move it and still get it into the box).
Being a thick foil, you may run into an issue with the back hitting the box and not being able to rotate the front of the fin enough to get the pin in place but the base looks small enough that it shouldn’t be an issue.
BUMP.
Since you have the original fin why not make a temprary repair them make a mold and cast a new one?
Fixing it would be easy, but I wouldn’t use this fin again, it’s too fragile. I think it’s about 43 years old, and made from Lexan. I think the best thing is to use this as a foil guide to make new fins with wood or foam side panels combined with glass.