I have seen two versions of NTP 179-160. The earlier is with NTP vca and the later one with sub board including DBX 2150 and some extra circuitry. That could be the difference that you are looking for.
The original NTP vca was quite expensive to build (lots of selected components) and it was replaced by DBX 2150 in their later designs. The sub board has some extra components to make 2150 pin to pin compatible with the old vca.