And to clarify further, it is not a "12 bolt" axle. The number of bolts refer to the bolts holding the ring gear to the carrier. It is coincidental that on Chevy axles the number of bolts on the rear cover matches the number of bolts on the ring gear. That is not normally the case for most rear axles. The Type O axle uses ten bolts to hold an 8.5" ring gear to the carrier. The Chevy 12 bolt uses 12 bolts to hold an 8.875" ring gear to the carrier. Completely different axles. Nothing interchanges.
62 F-85 Deluxe wagon (the NV desert car)
62 F-85 Deluxe wagon (the San Jose car)
64 Vista Cruiser
64 Jetstar 88 Conv
66 442 L-69 Conv
84 Custom Cruiser
86 Caprice wagon (w/307 Olds)