That appears to be a Huret-style dropout, so the RD can swing way too far forward. I'm kind of surprised it worked very well at all, but a guess a strong enough sprung upper pivot overcomes it.
Now, @
gugie can braze in a bit of metal to make it into a Campy-style, but not all of us have those skills. I'll bet you could glue something in there to make it work.