The scope ring mounts are cast as scallops into the top of the receiver, not on the heat shield.
His is a Ranch Rifle (with the scallops), yours is a Mini-14.
The rear sights are also different.
Mini-14
Thin barrel, ejector is in the bolt, no scope ring scallops cast into the receiver.
Beginning
Serial Nbr
181-07488--1978--1 in 10
181-48351--1979--1 in 10
181-84879--1980--1 in 10
182-45601--1981--1 in 10
183-03581--1982--1 in 10
183-40455--1983--1 in 10
184-17175--1984--1 in 10
184-26063--1985--1 in 10
184-95448--1986--1 in 10 and 1 in 7
185-14140--1987--1 in 7
185-50455--1988--1 in 7
185-56556--1989--1 in 7
185-81009--1990--1 in 7
186-05029--1991--1 in 7
186-18250--1992--1 in 7
186-20065--1993--1 in 7
186-31116--1994--1 in 7
186-42502--1995--1 in 7
186-58133--1996--1 in 7
186-66855--1997--1 in 7 and 1 in 9
186-81445--1998--1 in 9
186-87432--1999--1 in 9
*196-06325-2000--1 in 9
*196-44553-2001--1 in 9
*196-80982-2002--1 in 9
*196-99207-2003--1 in 9
*197-12180-2004--1 in 9
* Mini-14 serial numbers rollmarked with Mini-14 Ranch Rifles beginning in 2000
Ranch Rifle
Thin barrel, ejector in the bolt stop assembly, scope ring scallops cast into the receiver, buffer sytem using the recoil spring assembly.
Beginning
Serial Nbr
187-00001--1982--1 in 10
187-02611--1983--1 in 10
187-13218--1984--1 in 10
187-27226--1985--1 in 10
187-50919--1986--1 in 10 and 1 in 7
187-59308--1987--1 in 7
187-70033--1988--1 in 7
187-84127--1989--1 in 7
188-01157--1990--1 in 7
188-30499--1991--1 in 7
188-50902--1992--1 in 7
188-66901--1993--1 in 7
188-71086--1994--1 in 7
188-85981--1995--1 in 7
195-06037--1996--1 in 7
195-27761--1997--1 in 7 and 1 in 9
195-44221--1998--1 in 9
195-63542--1999--1 in 9
196-06325--2000--1 in 9
196-44553--2001--1 in 9
196-80982--2002--1 in 9
196-99207--2003--1 in 9
197-12180--2004--1 in 9