Check axle code stamped on the driver's side axle tube near the brakeline retainer, will be ZN if it's a 4 pinion axle. You may have to clean off the tube with a razor blade to find the code. I don't think any 3.55 axles were 2 pinion. 3.55 was the first of the performance axle ratios offered for all the Pontiac performance cars.
