In our province, in the old days (but not anymore), people often just dumped their old cars in the woods. That's where I have seen and recovered several of the 12 bolt axles I own. I have seen a lot of oddities during my parts exploration outings: 66 and 68 Pontiac sedans with 6 cyls and 12 bolts; 65 Pontiac CS HT with 6 cyl and 12 bolt; 3- 67 and 68 Chevy wagons (one 9 pass) with 283/307 and PG trans, and 10 bolt 4 arm suspension; and a pair of 69-70 Biscayne 4 dr sedans with 12 bolts. There is no rhyme nor reason that I can see, except that I was able to scavenge 15/16 front sway bars from all but 1 or 2 of the 12 bolt parts cars, which suggests to me that these also had the HD F40 suspension. .
Mine was built in January of 65, factory 12 327 250 horse powerglide 3.00:1 rear gear
It's interesting to see the changes of the "base" ratio over the years. Your 3.07 gear was common in 65 and as the chart at the top of this thread shows, it was still common in 66 but by 67 and later 2.73 became the ratio that was by far the most common in the b bodies. And not only did they reduce engine RPM doing the higher base ratio but the later year cars started coming with taller tires as well, reducing the RPM even more.
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1966 Strato Chief 2 door, 427 4 speed, 45,000 original miles
1966 Grande Parisienne, 396 1 of 23 factory air cars (now converted to a "factory" 4 speed)
