You must call Colt to find out.
1966
1971
Proofhouse.com has sn data.
With a G prefix, it is a Peacemaker and dates to 1972. The New Frontier sn would have NF at the end.
Nice revolver
1957
1972
Made in 1874.
Made in 1874
Proofhouse.com has Colt sn data.
made 1976
You must call Colt.