CCNL#339 has an SG subcontracted Inland receiver that's 20k earlier than yours and it has the L-379 slide. Carbine is a documented bringback.

A 1985 newsletter has another SG subcontracted receiver a few thousand later than the one above that has the early slide - and it has a later barrel date! (10-43). Looks like a case can be made that yours is in the transistion.

What is your barrel date and is the SG large or small?