After bumping into https://www.rx7club.com/1st-generati...+zinc+chromate and his 'old school' plating solution, I went looking on the site for a plating hints thread.
Not having found anything, I figured it might be helpful to someone to leave some hard won and even more 'old school' stuff. No pics available but shouldn't be needed.

Grubby small part(s) needs replating or repainting.

Materials needed
Demineralised water (for those in snow country, collect fresh snow and store in glass jars, the rest of us a good cloudburst again stored in glass jars - either will provide cheap clean water) which I'll call dmd water
WD-40
Hydrochloric or muriatic acid (it's the same thing) readily available as swimming pool acid or spirits of salts
Aircraft grade paint stripper for painted parts
Molasses
Laundry soap (the flake stuff usually is more agressive)
Glass bowls, pans or any other suitable sized glass container
A box of chocolates

Let's get into it

Start with a good spray of WD-40, leave for 2 or 3 days to work it's magic
Degrease to get the worst gunk off using a brass or stainless steel brush
Wash with laundry soap and scrub thoroughly
Wash with dmd water
[if a painted part, use paint stripper and wire brush, scraper, whatever works for you
[wash with dmd water

Now inspect carefully, if not free of all gunk (and possibly paint) repeat until it is.

Now it's time to remove rust the easy way.
Using a glass container (bowl or similar), make up a solution of 9 parts of dmd water and 1 part of molasses in sufficient quantity to submerge the part(s)
Put the part)s) in there, cover with plastic sheet and leave for 2 or 3 days.
Pull the part(s) out, wash in dmd water and inspect.
You should have nice clean rust free parts but repeat in the brew as needed.
Don't plan on storing this stuff for long, it will ferment a stink something wonderful.

We're getting close to plating, just need to final prep the part(s)
Again, using a glass bowl make up a solution of 2 to 4 per cent hydrochloric acid (no stronger!!)
Dip the parts in there for a few seconds, agitating gently, Zip or cable ties work well for 'handles'.
Wash thoroughly with dmd water.

At this point you could dry and paint the part(s) but personally I'd continue to plating and paint after that.

Go with the plating method linked above - it might be an old idea using vinegar and epsom salts but it works
One thing apparently not understood by the author of the above linked thread, the solution needs priming with zinc.
Some old dip or hot galvanized steel scrap will do nicely for this, just let the electrolyte solution etch away the zinc coat and the discard the rest

Immediately on removing part(s) from the plating tank, wash thoroughly in dmd water
Now this is where you need that box of chocolates, to pacify your partner.
You're going to dash into the kitchen where you've pre-heated the oven to 90 tp 140 degrees Celsius (no more) and put those parts in to the oven for 3 to 4 hours.
You're not drying them, you're doing something that really isn't essential for mild steel parts but is a good habit to develop.
The slow bake prevents hydrogen embrittlement in spring steel parts, particularly with chrome plating.

If you are painting the parts, primer with an etch primer meant for zinc.

There are solutions avaialble for yellow, blue and black chromate final finish from Caswell Plating and Jane Plating

Side thoughts - don't cut off the red wires from the computer power supply, join them together and leave for another time.
The colour code on a computer supply is black 0V, red 5V and yellow 12V
You can use 5V for anodisng aluminium.

Above all, remember that in plating cleanliness is essential.
Get into it and enjoy some really satusfying 'I done that' moments.