The term now used with SAI M1Aicon's is the 'golden age' rifles produced from 80's through very early '90s. They always had cast receivers, but in those years used a high percentage of GI surplus parts. Bolts, barrels, oprods ,trigger groups, sights etc. , and these are considered superior to rifles built using commercial parts since GI surplus has dwindled.
There are sites devoted to this rifle in all it's forms and manufacturer's .