Bill,
I am looking at your pictures and compare it to the one (not a Parker) on my bench and I can't see what is missing? The one on my bench has a pin in the screw so I can't back it all the way off but that's about all I see different.
I looked on the net at new ones too. See
http://www.woodcraft.com/Catalog/Pro...3-5dffdccb6eee and
http://www.woodcraft.com/Catalog/ProductPage.aspx?prodid=7764&ss=734c8766-c29c-47bd-88c3-5dffdccb6eee
If you bolt the back part to a bench and lube the guides it looks like your's should work?