How about just skipping the thumbhole configuration entirely?
In other words, get one of the several BATF-legal pistol grip stock conversion kits, from places like K-VAR or Soupbowl Enterprises, and dispense with that thumbhole abomination. Then your MAK90 can operate and feel like it was originally configured, save of course for the full auto notch on the safety lever...
I have a Choate Dragunov stock on my AK and I love it. It is very solid and very comfortable. I have tried most of the thumbhole stocks on the market and the Choate is the best.
I like it so much that I have not yet put in a US parts kit so that I can use the standard 2 piece stock.
If you do decide to replace the hammer, trigger, sear and go with an "authentic" stock I would recommend the KVar US made synthetic stock. It replicates the Bulgarian GI stock but is a little longer to fit Americans. It is a well made, very comfortable stock. If you go this route you really should replace the lower stock tang that was eliminated to fit the thumbhole stock.
Or, you can get an Ace skeleton stock. It is the fixed version of their side folder design. It is very rugged, of proper length and looks pretty good. Their mounting block accomodates for the abscence of the lower tang.