I think you need to start over. The links are dead, the text shown is not helpful enough
You need to get some photos posted and SLOOOOW DOWN!
It sounds like you want to change your gears in your rear end.
Based on this info from FBBO you have an 69 to 70 8.25.
Casting# Year Body Size Notes
2070051 1960 - 71 A 7.25 9 bolt cover
2070062 1970 - 71 A 7.25
3507881 1972 - 74 A 7.25
2852905 1969 - 70 B 8.25 10 bolt cover
3723598 1971 - 74 B 8.25
3723599 1971 - 74 B 8.25
1634985 1957 - 67 ABCD 8.75 10 studs/no rear cover
1820657 1958 - 64 C 8.75
2070741 1964 - 74 ABCE 8.75
2070742 1959 - 68 BCD 8.75
2881489 1969 - 74 ABCE 8.75
3507890 1973 - 74 B 9.25 12 bolt cover
3507891 1973 - 74 B 9.25
Dana 60 1966 - 72 B 9.75 10 bolt cover
Dana 60 1970 - 71 E 9.75
You should call Dr. Diff he will know how to help you.
Good luck
