Just down the board is a huge thread on Rome in Limo, a wonderful company that operates in Naples, as well as other Italian ports. There are tons of recommendations there.
Viator is a broker...they don't provide the actual tour. It is commonly discussed here that it is better for everyone to deal direct with local vendors to provide your desired tour.
One of the benefits of working directly with a local vendor is that a vendor can build custom tours. Viator (and the several other brokers commonly mentioned here) will provide an out of the box, cookie cutter tour. If it is possible to visit the locations you desire, considering time and local conditions, the vendor, like Rome in Limo, will make it happen.