If your car was an original small block you more than likely have the 8 1/4".
Do you see bolts around the inspection cover, on back of the housing, when looking under the car from the rear? if so ya got 8 1/4.
An 8 3/4 does not have an inspection cover and the gear or center section bolts up from the front.
How long have ya been the owner of that car?
I remember responding to a craigslist add about a guy looking for 71-72 Satellite/Roadrunner parts but lost the persons email addy.
That wasn't you was it?
Sorry if it was...
I don't really have any small block parts, I might have some connections tho, if ya still need.
Anyways what area are you located?
I'm just northeast of Detroit by the lake.