Thanks for all the ad-vise. Lots of options. I decided to ry drilling the screws out enough to get the jaws off and so far, so good. Now all that remains is to get the remains of the screws out. Now that the screw stubs are exposed, I'm going to let Kroil do its thing for a day or so.
I was able to put the stationary jaw in my drill press. Being slot-head rather than Phillips, and a couple being somewhat mangled, they were a little more difficult to centre punch to start drilling. I ended up using a 1/4" carbide bit from my die grinder to start the hole, initially a tapered one then a ball-end, followed by a 1/4" cobalt drill, then a 3/16". After that I was able to knock the jaws loose with a cold chisel. Those screws were pretty well rusted in.
The dynamic jaw wouldn't fit in the drill press so I had to drill freehand but it still turned out OK. I omitted the 3/16" bit as I realized I only had to drill the flat head off the screw and not go down to the base of the jaw.
