old wallet few years old, had to do clean install of bitcoin core and made few copies of old wallet files across 3 computer for safety.
so the old wallet.dat file should by restored to bitcoin core//app data folder prior to sync of wallet? or can the old wallet.dat file be imported later after sync of the wallet?
are there any other files that need to be replaced?
Unless your wallet.dat is of a very old version of Bitcoin Core (should work too) the only thing you need to do is to copy paste the directory with all the bitcoin data in it. In newest version it is simple "Bitcoin" and it is where the guy in the post above described you in the appdata\Roaming\Bitcoin. Simply copy the wallet.dat in this directory, run Bitcoin core and it should work.
If not try to start Bitcoin Core with -salvagewallet option.