I am using a 6" Bridgeport vise on my mill. I restored it. It too was missing the jaws. Other than that, it mostly just looked really bad. I disassembled and cleaned it up and stripped the paint. The vise has box ways, like higher end milling machine saddles. You can scrape the sole and scrape the bottoms of the extended sides of the movable jaws (where the boxing plates mount) to tighten up the fit. My beat up (50 year old?) vise still had only .0015" of vertical clearance in the worst corner, with a little work it is now at .0005" clearance along the entire bed. I have used Kurt vises, and my Bridgeport holds work down without the movable jaw and work rising better that the Kurt does. I also like the solid sole of the vise, no voids for stuff to fall into. The acme screw is high and exposed and it is easy to keep it and the bearings clean and oiled. Those old Bridgeport vises are very nicely made, quality tools.
I made the jaws from 1/2 x 2" 1018 cold rolled bar stock and finish machined them in place. I prefer softer jaws over hardened ones. They grip better. They can easily be re-machined if they get dinged and are also easily and cheaply replaced. I bought a 3'+ bar of the 1018 and that is likely a lifetime supply of vise jaws.
I also made keys for the slots under the vise and made them a snug fit in both the vise and the table slots. With a little wiggle the vise drops gently onto the table and into the slots and is within less than .001" of perfect tram over 6" by just bolting it down. A simple tap with the palm of my hand in the correct direction before tightening it down gives less than .0005" runout in 6", without using an indicator at all.
I guess you can tell that I am happy with it...