If you have a Mill then removing these cast in jaws are not to difficult. The secret is Rigidity of Setup. What I mean is the vise has to be tied down tight and the Dynamic shimmed equally on three sides using feeler gages (top and both sides) and the Dynamic tightened on a spacer block right under the jaw towers. A little bit of hand work on the block to fit the casting, I like to use Aluminum.
Align the Static with a indicator and I know the needle bounces but moving slow you can align it pretty good. then I like to find center of the two jaws. I sweep the center in with a indicator but a edge finder works too. The reason I find center of the opening is that I cut the jaw side depth to the same numbers so the same thickness jaws will look even when installed.
When you are ready to remove the jaws I have found using the side of a carbide endmill gave me the best results. I purchase 10 3/8 carbide endmills for a $100 and use them for this cut. I can get by with ruining two cutters per vise. As for the cut I use a machine with no backlash so I can cut conventual or a climb cut. If using a Bridgeport type machine then Climb cut is the only way I would cut due to having the cutter pull into the work. Any vibration would chip the edges. I go .010 per cut lift the cutter go back and dial in another .010. and I like using coolant. Note the hard material showing up when getting close to cast material, I added a pic. The tool pressure will be noticeable when you reach cast material. Most cast in jaws are 1/2″ deep, the Reeds have a special hard insert with undercuts and watching the cut you will see when the hard material is removed. The hard material must be removed so drilling and tapping holes is easier and you are not drilling into hard material.
I am a jaw builder so I had plenty of jaw choices, sometimes I have to build a custom jaw but I try to fit a set of Wilton jaws since they are still available to purchase. I like to have at least a 1/16th to an 1/8″ above the jaw towers to hand finish the tops, some jaws I radius the tops by hand and some I like them to be flat across. Cut your depth to the correct number. I always use a brand new endmill for the finish cuts, this ensures a straight wall for the back side of your jaws.
I will note that if you are clamping a stationary vise to your table you must first flatten the base. If not then shimming is needed and that is trouble with all the tool pressure needed in removing the hard jaws. I like to level the slide surface above the dove tails that the slide sits on. I use a long precision parallel and use a indicator to level the vise. Having the base parallel to the slide keeps the jaw cuts perpendicular to the slide. Every vise has a different method of clamping to your mill. I do not think I tied down the Static the same way on two vises. Make sure it is ridged and always cut in a direction that will not grab and pull the vise into the cutter if it comes loose.
Once the jaw pockets are cut then adding the tapped holes is the next step. One way is to use the jaws as a guide and try by hand to drill the tap drill size hole straight and centered and not all the wat thru, if doing it this way I like to clamp the jaws in place and stake the center with spotting punches. I would spot one hole then drill and tap then add a screw in the first hole and do the other side. I have got away doing it this way on very big vises that would not fit in my mill. The preferred way is using a Bridgeport type machine and a large angle plate to clamp the Dynamic or Static in place. First I indicate the jaw face flat then align the jaw shoulder perpendicular so everything is square and parallel. Then I find the jaw shoulder with a edge finder and move to the center of the jaw screw hole. Then find center of the vise either with a indicator or a edge finder. It is important to have the threaded holes centered to the vise so the jaws are not sticking out on one side and not the other.
This method works for me. Getting these old quality vises back in shape gives you a good feeling and makes the vise’s worth much more.