Did you ever have any luck on finding spare parts for this vise?
I have this same vise and received it new in 1998 or so. As for your model, I don't think you're missing anything because my vise backs out all the way without any type of safety catch.
I have this model vise from 1997. It's the Columbian D4 D54 Vise with 4.5" Jaws. I'm actually looking for replacement jaws if anyone knows where I could find some that would be awesome.