A factory Slant 6 with a 8 1/4 differential

i think that because your car has front discs is why you have an 8 1/4 which as far as i can figure out would be possible from the factory. I've seen a few cars around like yours and all the /6 cars that had disc brakes (that i've seen) had an 8 1/4 instead of the 7 1/4. can anyone else confirm???