Look back at the picture of the underside of the bench. I'll refer to various locations on the pic. The fixed jaw (that you see in the upper right corner) is fastened to the bench skirt with two #10 2" screws through the jaw and into the skirt. The rear support is fastened between the side skirt (top of the pic) and the cross-member (bottom of the pic) with two each #10 2" screws through the skirt into the end of the rear support, and through the cross-member into the other end of the rear support (where the broken shim is seen).
The threaded flange of the bench screw is fastened to the inside surface of the bench skirt with #10 2" screws, the heads of which you can see in the pic. That's what references the position of the movable jaw.
What is missing is the front plate, which will be split in half and have a centered 3/4" hole that will capture the bench screw in the 1/4" groove (visible in the picture below) just behind the handle. That will pull the movable jaw out and the other side, as you observed, will push it in.
The 1/4" thick front plate may be inlaid into the front jaw (if I get ambitious -- otherwise it'll be surface-mounted) and there will be a 1/8" recess just behind the plate to accommodate the 1 1/4" diameter flange on the bench screw behind the plate.
The bench screw was obtained from Grizzly for $33.00 plus shipping. There are other options, including an Acme-threaded hardwood dowel, examples of which can be found on the Internet.
Hope that clears it up and I apologize for not making it more clear.
And I'm vacillating between a 3 1/2" round plate (made of a 1/4" thick fender washer) or a 6" long by 3" high plate made of 4 gauge steel...IF I can find a machine shop that will do such a small job.
Last edited by 163481; 08-16-2017 at 06:45 PM.