Yes, the '76s and '77s used the same rear axle code. ('68 and '69 use
similar but not identical codes; '70 and '71 each has its own; '72-'75
are one series; '76-'77 are another; '78 and '79 each have its own. My
source book doesn't go beyond '79...) There are common codes between
some of these sets though.

As to manufacturer, it appears that Eaton made the rears from '64
through at least '79. '64 seems to be a mixed year with some rears
coming from Dana. I'm looking at a '53-'79 Corvette Chassis and Body
Parts Catalog I scrounged from my local dealer 25 years ago. All the
rear end components that I see that are identified by maker indicate
Eaton parts for '65 and after.

Here's waving to ya - \||||

Owen
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'67BB & '72BB
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"To know the world intimately is the beginning of caring."
    -- Ann Hayman Zwinger