rear end swap

[73-charger-383]

Looking to replace the 8 1/4 rear in my car with a 8 3/4.  In trying to find an interchange, I found that the 1970 c-body's used the same rear (dimensions wise anyways).  Thing is, there's a 1969 Monaco for sale local with the 8 3/4.  In looking at the body styles, in 1969 it's the same platform that continued out into the 70's.  - any have any insight as to why the 1969 Monaco rear wouldn't be the same as the 1970 Monaco?  I know the 68's wouldn't work as they are a whole different car all-together, but it's looking like a bunch of these sources saying that it's 1970 and up should actually be 1969 +....any thoughts?

[Nacho-RT74]

althought there are websites with more detailed information, extracted ( or scanned ) from interchangability books, this table uses to be the easier to read and accepted everywhere as a valid info