George,
This subject has been pretty well covered, so just additional affirmation from a former ARC LS16 owner:
- The Wonder InfiniCaps™ are definitely stock.
- The ARC Database is a wonderful reference tool but know it is not in any way affiliated with the Audio Research Corporation.
- If you plan on keeping your LS16 for a while then another vote for atmasphere’s (always) sage advice. Have the filter capacitors replaced and consider it preventative maintenance.
- Although not brought up, if you go looking for a phono preamplifier the ARC PH3 made an excellent and very synergistic combination with the LS16. The PH3 utilizes three 6922’s, same tube as your LS16.