I've come across an interesting (different) speedometer error on the '70. Drive/driven gears are correct for the differential gears and tire size. The odometer is correct. Most of the time speedometer error is linear. This is not.

Speedometer - Actual

18 mph - 30 mph
30 mph - 40 mph
36 mph - 45 mph
40 mph - 48 mph
48 mph - 55 mph
59 mph - 65 mph

Somewhere around 85 mph the speedometer matches the actual.

Anyone else had a similar problem/solution?