Thx Jangle,
As Wayne mentioned, Inlands first serial number block is covered in CCNL 346. Looking at page 14 there is mention of Niedner Rifle Corporation having produced the N and NI marked Front sights. 2 Inland carbines having NI front sights were reported in CCNL 346, Serial #'s 327,7xx and 607,763. Now we can add Jangle's 291,8xx. CCNL 343-2 has a picture of a NI front sight.
Also some SI marked front sights made by R.F. Sedgley Inc were found in the 1st block between 34,512 and 564,718. Some SI front sights were also reported in the Sub Contract Supplied S.G. receivers to Inland in the 704,585 to 887,6xx range.
The snip it below dates back to when USGIBOB and Bruce still had hair, wearing Bell bottom pants, platform shoes and listening to the Bee Gees while dancing to Saturday Night Fever
From CCNL 32 from June 1979, reported by J.B. Powers.