You have it fairly well right.
People seem to have a problem working out the difference between a scarrifier & a lawn mower.
Mower companies pander to this by making decks that go lower that 2" which is the lowest you should ever cut grass.
The nuts that hold the pulleys down tight on the spindles have a cut away so they can clear the end of the shaft and clamp tight onto the pulleys.
The wrong nuts will not hold the pulleys tight and they will strip out.
There are a couple of different blade mounts.
One will allow some slip when you hit something solid, the other 2 won't.
The deck should have anti scalp wheels to prevent the blades becoming plough discs.
There are a few different spindle housings that will bolt up to the deck, some are more expensive that others and some hold the blades lower than others .
Being it is a used mower, you have no idea what is on there.,
So your first stop, is the JD web page for a copy of your deck parts.
You can print out the page strait off the web , but not the entire book.
Then have a look at what should be there against what is currently there.