What to do with orignal valve covers

They look remarkably good. Keep in mind that the OEM chrome finish was marginal at best. How about just using some good chrome polish like Mothers or Maguires from time to time to keep them looking nice.

Yep, those look pretty decent in those photos.  Your own idea was what my suggestion was going to be - a lightly oiled rag every little while.

I'm sure that for far less than chrome plating, you could have them chrome powder coated.  Do a search for 'cudachick' online and you'll find Phoenix Specialty coatings.  I'm sure she'll be happy to give a quote based on some emailed pictures.

Nicely done - vinegar is useful as a mild acid for rust removal and very very slow removal of certain metals. It's a good cleaner, too, being organic it has the ability to remove oils and grease, other "scums" as well as rust removal without harm to the good surfaces.
I was at a wood-working seminar where they showed restoring and cleaning older hand tools using vinegar.
Soak your old metal files in it and it can help restore some of the sharpness as it very slowly eats a fine layer off of them, resulting in sharper cutting edges, not to mention removing the rust and dirt.

I thought this was done and settled in another thread in which Steve P and Chuck Page participated, demonstrating exactly what AMC valve covers were finished in and how to use modern methods to duplicate that finish. (It's actually easier in a way but that's another little detail.) Fact is - AMC valve covers are Chrome. The prior thread more than proved that, and now that I do plating myself, I'll also further confirm they are indeed chrome. For one thing, the biggest "tell" is the bloody color! There's a big color difference between nickel and chrome and just seeing two sitting side-by-side is enough to tell those without colour-blindness that they are finished in chrome due to the white or blue-white color. Nickel is yellow. Chrome has a blue-white cast to it. It's really that simple.
But for the non-believers that persist............. here's more:

The process has been shown, demonstrated and proven.
Nickel will tarnish and is more yellow.
The chrome protects the nickel and adds the blue-white cast to it.

It's not lack of polishing the chrome that gives it that look - it's simply that they used a plating bath closer to the Watts bath than the shiny or bright nickel plating done for under show chrome.
Nickel wouldn't last and would be yellow without that chrome plating on it.
There are multiple types of plating baths - for the basics there's alkaline, acid, and multiple in between, and even in those categories there are variations of baths made different by the metal salts used, chlorides, oxides, brighteners, wetters, etc. 
I can vary the color of nickel, zinc, etc. all by the bath, time in the bath, amperage used, ph/acidity, number of "coats" and so on. If you polish between multiple "coats" you can get a really deep shine with a bright bath. Or use a non-bright bath and get what AMC got, then apply the chrome and you have it!
AMC took the bare steel covers, activated them, put on a non-bright nickel plate and then chrome.
There is some polishing and hand work for perfect finishes, but seriously a lot of it is also in the bath type used and in AMC's case, had they used a bright nickel bath with the right additives the valve covers could have been really shiny WITHOUT polishing! Organics such as dextrin, SUGAR, and so on can act as brighteners by making the metal crystal formation finer.
The reason most shops today have trouble duplicating that look is that they don't have the other bath types due to there being no demand for satin finishes on car parts. Their plating baths are extremely expensive and to keep a tank of Watts bath or some other non-bright bath for a satin finish when 99.95% of their customers want shine would be silly. The bath type is the biggest factor in that finish, lack of polishing is secondary and that's why the trouble finding anyone to duplicate the finish.
 
Back on one other part of the older conversation on valve cover plating - actually, I CAN make pitted or non-perfect metal turn out with a smooth finish and shine, too - with a little work.
(The word little being sort of sarcastic as it can take many hours.) I took a very badly marked up wiper motor frame/housing and filed and sanded the imperfections, plated multiple times  hand-finishing each layer down to smooth before the next and you now can't tell it was badly marked and gouged. Did the same for a wiper motor mounting plate - the pits are no longer visible but you can't afford it...........there's 2 days of work into that single part.

Personal experience -
I've done nickel plating recently - it isn't at all the same color metal as an AMC valve cover.
I've been in the plating forums where the professionals hang out and ask or answer questions - they also confirmed these are chrome. I've dealt with the chemical and equipment suppliers/vendors myself in recent months.

Since chrome doesn't adhere directly to steel - you put nickel beneath it. (There's a chart one can use to help determine what metals are more active, which are more passive and thus you can determine what is likely to plate onto another metal)
It's the nickel that gives a good chrome plating its shine and smoothness. It's not the chrome that shines and looks nice.

I have posted photos in the other threads here showing nickel and chrome color differences and how to tell them apart. But it's hard for science to fight urban myth and legend and those who are most vocal in their insistence.

Here is a bright nickel finish done with an acid bright nickel solution - compare to the WHITE or blue-white of AMC valve covers. (or refer to the photos I posted a couple of years ago showing the differences on actual valve covers)
Of course depending on the amperage used, the solution type and so on, you can make the color more or less "yellow" even in nickel, but never get it to the white or blue-white of chrome.
(I did not do these but know who did)



(I challenge anyone to scientifically prove otherwise - that AMC didn't have chrome on these covers, and not with a he said or she said or my brother's wife's Uncle Bubba said so but with proof, evidence other than legend.)

Here's an example on finishes determined by the type of plating, methods used, amps, etc.

Here's a shiny part - zinc -


Here is the same type of part, it is also zinc, but "satin" finish.
The only difference is the plating bath and method used, not the polishing done -

The vinegar procedure worked so well, decided to submerge the intake manifold and see what happens. A lot of crud was in the Home Depot plastic storage container after 48 hours, but what a difference!

"Just clean them real well then shoot them with a coat or two of high temp clear." X2