Nothing at all wrong with grinding a couple of thou off the base to rescue them.

Or even a bit of firm polishing with green 'scotchbrite' scouring pads. If case hardened, the case may not be very thick.

That's what I'd start with, plus WD40 to lubricate. Least chance of disturbing any original dimensions.

Then use fine 1500 grit emery paper on a surface plate if you're still not happy.

Only go to grinding and removing measurable amounts of material if necessary and (economical or piece has sentimental value).

Good grief! That's not corroded! Stone it off with a diamond lap or similar with some thin oil – or Scotchbrite You would be surprised how hard it is to remove significant amounts of steel with a fine abrasive, and certainly for the kind of job a surface gauge does it won't have any effect.

The corrosion is little more than pitting, a very high percentage of the surface is still there.

As working tools rather than exhibition exhibits, I would feel inclined to follow the Scotchbrite route, to ensure that there is nothing protruding above the surface.

Not perfect, but will do the job quite well, possibly better than regrinds, if the case hardening were to be removed.

Grinding costs would probably exceed value, and could make the bases worse, in terms of accuracy or durability, than if just cleaned up.

Howard