I've never seen or heard of an 8-bolt rear ?
Got any pictures?
There WAS a 9-bolt, but I only heard of it being used in GM's F-body line.
The V-6 was only installed as an option in the 1978 through 1987 ElCamino's.
The ElCamino is a "G" body, sharing it's stock 10-bolt 7.5 inch ring gear equipped axle with the following.
(assuming you are dealing with a vehicle manufactured between 1978 and 1987)
Monte Carlo, Malibu, ElCamino (and GMC Sprint)
Century, Regal (RWD only), GNX and Grand National (highly prized for having the 8.5 inch 10-bolt axle)
Cutlass, 442, Hurst
Lemans, Bonneville (the smaller version, the "B" body bigger version WON'T fit)