Near as I can tell, General Mao has never used a 4¼" bolt pattern. GM's car bolt pattern is 5 on 4¾"--larger than Chrysler, Ford, and AMC's 5 on 4½". The Mopar "BVD" bolt pattern is 5 on 4". Ford used the oddball 4¼" pattern on some RWD cars, but as far as I'm aware they were all IRS (Thunderbird, Mark VIII, Continental). The Eagle Premier/Dodge Monaco twins used it, too, but they were FWD.
Whatever the axle is, it ain't a GM 8.2" unless you're off on the measurement.
All A-body 8¾" axles share the same dimensions from 1965-'72 (supposedly 50 1965 cars were built with it for homologation) and fit models through 1976. The 8¼" was first used in 1969 B-bodies, but didn't appear in A-bodies until '73.
The 8¼" just isn't worth the effort to narrow it. The labor & material are less to narrow a C-body/truck 8¾", which is far stronger.