It's not really a version 6, it's probably better to just call it the ARES Tavor mechbox.
Standard linear nozzle, no indexing feature. Not sure what the air nozzle dimensions are off hand, there are many different nozzle lengths in existence. The trick is picking the right length.
The piston head is standard v2/3/everything. The piston is classic Marui profile (non-side-reinforced first tooth).
ARES makes a replacement top rail and side rail.
http://www.aresairsoft.com/home.html