Take it apart. You may not be able to get the one remaining vise jaw off yet. If not don't worry about it for now. Once it's apart, you can put one part at a time into a big pot of water with Cascade dishwashing detergent in it (quite a bit). Heat it until the whole pot simmers, then hold that temp for 1-2 hours. Remove it from the pot and pressure wash it. After that, go over it with a wire brush (cup-type with twisted wires on an angle grinder).
That should pretty much take it down to bare metal except for interior spaces where the grinder can't reach. Then you can decide what to do with the rusted-on jaw. Sandblasting won't help you get the one jaw off if the screws are frozen. At that point I'd do electrolytic derusting or you can dunk the part with the jaw into a container of Evaporust. Either of those will likely remove the rust to the point where you can get the one rusty jaw off. You will have one pair of factory jaw screws to measure up. You may not be able to buy off-the-shelf replacement screws. However, since you are going to have to make new jaws anyway, just design them to use socket head cap screws.
If you can afford it, machine the new jaws from A2 tool steel. Then heat treat it (the good thing about air-hardening steel is you only have to get it hot, don't have to quench it, just cooling in air will harden it) and temper it as desired, then the jaws need to go onto the surface grinder to be ground to final size, parallel and square. Don't forget to check that both your fixed jaw and moving jaw have the same exact screw location because sometimes they don't. You can drill and tap new jaw screw holes if you need to.
Then look at the vise screw assembly. It may need new pins if it's a Wilton-style, or it might need the nut derusted, or something might be cracked or missing. Fix everything, making sure the screw turns smoothly and solidly through its whole range. Make a new handle. I like to make my vise handle a bit longer than stock. I turn down the ends to a shoulder in about 3/4", then bore holes in two pieces of bar of larger diameter than the handle stock so they can slide over the turned-down handle ends and bottom out on the shoulder. I make mine about 1" deep, so the handle end is recessed about 1/4". Put the handle through the vise screw, turn it vertical and plug weld the end pieces to the handle. If you want, you can grind them smooth. This is easy and fast and super strong. If you want to go deluxe, get a pair of thick rubber washers waterjet cut to size, and stretch them like rubber bands over the heads until they sit neatly around the handle. That might save your hand from getting a bad pinch.
Now mask it and paint it and do final assembly and then you will have your 100 year heirloom.
Here's what my most recent restoration of a big vise looked like after it was done:
Oh, and one last thing. Reduce the size of your pictures before you post them!
Good luck,
metalmagpie
