Nice group! I need to get one. I've been using a Milford Midget mini hacksaw for most saw jobs, but it's not a keyhole saw.
I wonder if the saw blade of the Stanley Handyman will fit in a fixed blade utility knife? I found a 1960s carpentry book around the house (it's been my go-to for some beginning projects), and it shows a Stanley fixed blade utility knife with a similar saw blade installed in the handle. With that hole in the center and the notch at the spine of the blade towards the back, it looks like it might.