I'm working on bringing my AKM into the classic AKM configuration, right now it has a synthetic stock and a parkerized finish.
I'm gonna put a laminated stock on the rifle, and I'm considering upgrading the finish. Duracoat or Cerakote etc...  
In the pictures of older military AKMs they appear to have a darker finish.  Were the rifles painted?  If so what kind of finish was on the rifles? Satin, Matte, Semigloss?

It depends on where and when they were made, but Euro AKMs were mostly finished in bake-on paint. China blued theirs. I think it was Poland that used bake-on paint over Parkerizing. Etc., etc.
ETA: The painted ones would have a flatter finish for the military. For the most part, when they began to import complete semi-auto rifles from Hungary, Bulgaria and any other Euro countries, the finish was a little brighter. Then, after '94 when the 'sporters' came in, most of those had a gloss finish. So, the 'correct' finish depends on a lot of variables.

Yes, they were painted with a bake on finish. Check out the Russian parts kits for sale on gun joker. They're good examples. I know of a guy who sells the paint on another board. Seems to be legit, but he's overseas.

There is evidence that some of the Russian guns were painted by hand with this. I can't be sure on the method.