1974 Fender tags and rear ends

Well, crap! I ckd under my 74 Valiant Brougham and was hoping it might be at least the 81/4 because it did come stock with the 318, but it sure looks (by the rear end spotters guide) more like a 71/4. Is there anywhere on the fender tag I can see what originally came under there? Any advice? anywhere reputable places to score a 81/4 or better without leaving the family destitute? Im really kind of stuck now, it looks like my mild sleeper Duster project may be more of a pud when it all said and done.... :scratch: