I'm gonna say that's a Dehavilland repair or school facility.
Take a look at GTX's picture again.
Notice the spars. Notice how they taper down towards the left of the picture, but the thicker sections are to the right.
In those days, the thinking was still that the teardrop shape was the most aerodynamic.
Initially, I thought she was drilling from the rudder into the vertical stabilizer, but look closely at that pictue.
It's actually the other way around.
So what does that have to do with Dehavilland?
I give you, the DH.95 Flamingo....
...look very closely at the tail section. Notice how much of the vertical stabilizer is rudder.
To me, it looks just like what Ruby May is working on.
"But it can't be, we don't see the cutaway and attachments for the trim tabs!" You say?
That's because GTX's picture doesn't show enough of that part of the tail. Those trim tabs would be outside of the picture.
Remember,
trailing edge is towards the left (where the trim tabs would locate), the
leading edge is towards the right of that picture.
"But its a transport! That rudder woud be HUGE!" You say?
The Flamingo wasn't
that large. According to Wiki, it grossed out to only 18K lbs. About the same as a Lodestar.
So, I say it's the rudder from a DH.95. That's what I think anyway.