I've had a very good look at these lately. The differences that immediately come to mind are that many of the 858's were built using modified select fire receivers as used by the military. They had a couple of small steel blocks welded to the inside of the receiver in specific areas to prevent the installation of certain original unmodified trigger parts. They also appear to have been remarked by the factory. If you've seen one with the original Military markings you'll see the difference.
The CSA or VZ58 has a new commercially manufactured receiver that is machined in such a way that the select fire trigger parts cannot be installed. All other parts ie. barrel, bolt, bolt carrier etc. appear to be the same. Most of the CSA VZ 58's I've seen lately come with the mod to the bolt carrier to prevent the dreaded "Gremlin".
Other than different Stocking options, the only other main difference is in how the safety operates. On the VZ858, the tail of the safety faces the shooter in the firing position, and is pushed downward and forward from the rear to engage Safe. The VZ58 has the tail facing forward in the firing position, and is pulled downward and back to engage Safe.
The other main difference is the price. The VZ858's were around $700.00 the VZ58's are around $1000.00.