LP wrote:

I have an offset wrench for my router such as the ones at the bottom
of this page:

http://www.woodpeck.com/plungelift.html

Actually I have two of these. The first one, even tho clearly marked
as 24mm measured closer to 27, and the 2nd, also marked as 24mm
measures 25.

The first one I didn't use at all, and the 2nd I used only long enough
to find out it's too big. Even with this minimal use tho, the jaws
are clearly deformed which makes me think it's made from pretty soft
steel.

My thought is to MIG a weld bead along the jaws and then regrind to
the correct size.

My question is, would this bead be hard enough to function in this
application, or do I need to further harden the whole thing?

If hardening is necessary I'd appreciate a quick how-to, since my
memories of this procedure are quite vague.
I would get a real wrench that fits and bend it.