Limited slip, posi and spool, how to tell which?

[Jeff H]

On my 70 L78 Camaro a lot of people have noticed how one of the rear wheels tends to hop when I'm making a turn into a parking spot. I can feel it and thought it was part of the clutch issues I'm having. When I jacked the car up and turned the wheels to verify the gears it came back as 3.55 turns to 1 and I noticed that both rear wheels seem to be locked together with absolutely no slip at all. Does this sound like a spool or posi? I know it can't be limited slip. Also, the car has an HEI distributor and runs great. But the tach is reading around 3500 rpm's at around 62-65 mph. The tires are 245/60/15 and that would work out to 4.56 gears but I'm positive they are 3.55 gears. Would the HEI cause the tach to read that far off. The speedometer is reading around 50-52 when I'm doing 62-65 and I assumed it was the speedo gear was wrong. Thanks for any help. I'm not into racing so I can't really tell for sure.