I have a yugo SKS and all I want is a scout mount that leaves the ironsights alone. As in no tools to remove. Would it be legal to replace the upper handguard with a synthetic piece with a picatinny rail?
If the bayonet screws off, I'd say it wouldn't be considered permanent. However, removing the grenade launching adapter would be considered permanent, IMHO.
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.