Regards Inland Handguards, I can report what is in the CC newsletter 361 which examines Inland block 4897526-5549821. on Handguards it says- the block started out with usage of two rivet shallow groove handguard. The earliest report of a four rivet handguard was around 5,179,xxx. After that the two rivet was only occasionally reported. Markings on handguards include H.I. and OI