Everything got here complete and fast, but, like you thought, the ServoStiks are non-standard JLWs.
Here is a comparison from the side.
From the left: JLF (hollow), stock shaft from the ServoStik (not hollow), new JLW (hollow).

From the bottom down.
From the left: JLF (hollow), stock shaft from the ServoStik (not hollow), new JLW (hollow).

The length is correct with the replacements, the top half width is irrelevant, but the stock ones are too skinny at the bottom.
So I'm going to try to put it in a drill, and "lathe" it down to size with sand paper. Wish me luck.
This is of course after I mixed every stick and shaft I had laying around to try to get it to work, but no.
I could try to drill out the pivot (little half-ball thing) but its solid metal, the black spring keeper wouldn't be a big deal as it is plastic.
I'm going to try the lathe method, as I bought some 10mm threaded shafts I can practice on.