The nickel finish looks pretty good at least in the pics.
There's a good chance the metal surfaces underneath are in decent shape too,,no deep pitting, etc. that would show even with the nickel over the top.

There is a way to laboriously copper plate and then flat polish it down leaving the copper plate to build up in the pitted areas till it's level with the base metal. Then copper plate once more and then do the nickel.
That done well, will hide the pits.
So will filling the pits with the 95/5 soft solder that is tin/silver. The alloy will accept plating well and the technique is much easier than the former.

I understand that some mfg'rs used to 'save' some frames and major parts by filling voids and scars with 'braze' (brass). Same idea as above and plate over it.

It might take a bit more polishing than starting with 400g to get the surface you want.
Re-establishing edges and polishing flats, you might have to start back a couple grits, but if rust bluing, there is really no need to go much finer than 320g. That unless you can juggle the bluing technique to save the higher polish along with getting the bluing. It can be done.

Neat project!
I'm working (slowly) on a 1917 that was terribly buffed and reblued and the Military markings removed with files.
25+ hrs of polishing to get it to the point of 'what to do with it now'..

I like to use those Diamond Lap sticks for a lot of polishing. They don't load up and used with a bit of oil they cut smoothly, aggressivly & keep things flat.