Since my chances of being able to acquire a real INSAS are basically zero, I'm trying to collect enough information to build a replica. CC's breakdown was very helpful, but I could still use some more pictures of the rear sight block and gas block.
The most complex part looks like it would be the rear sight block and cocking handle. I have the capability of making or modifying the metal parts as needed, but I would probably have to do the furniture in wood and declare it "close enough."
There are some rifles that diverge at least as far from the basic Kalashnikov AKM - the Valmet, PSL, and the Saigas come to mind - but they're also quite well known and well-documented. Heck, there's even a reasonable amount of information about the South African CR-21, and those never actually went into production.
By contrast, the INSAS is almost unknown outside of India, and almost all the useful information about them (that I've found, anyway) is in a couple of threads right here.