yep, definitely way off. I had the same rear gears and tire size in a (4-speed) A-body some years back, and 60 mph = 2600 rpm.

As others have pointed out, you have too many "variables". First you need to know if the tach is accurate. You already found the speedo to be nearly 10% off. Once those are both calibrated, then if it's still high the only thing left is converter slippage.