WHATS THE STOCK UNIT 8.5?
it depends if it's a 10 bolt or a 12 bolt. just count how many bolts hold tho cover on.
My 79 had a 7.5 inch in it
I know this is a bit late, but all 1976 Malibus came with the 8.5" 10 bolt. Posi would be denoted by RPO G80 on your build sheet. Sometimes the tag will still be on the differential.