This is a very grey area. The general consensus is that removing the bayonet, grenade launcher and night sights (all three), removes the rifle from C&R status, yet this configuration does not violate 922(r), so it is still legal. Removing only two of the three makes the rifle illegal.
Unfortunately, ATF never gives a concise answer on the subject and never sticks to any answer they do give. For example, some say removing the bayonet is good enough while others say the bayonet lugs need to be removed as well.
There is some reading on the subject: http://www.victorinc.com/SKS-FAQ.html#_Toc167103932
The safest thing to do is to send a written letter to ATF stating what you indend to do to your SKS and get a written reply from them.