Easiest way to tell on '80-'81 cars is to pull the speedo out of the cluster and check the mileage on the o2 sensor's mileage drum. It is not visible from outside the cluster, I didn't even know they existed until I swapped my 85+ mph unit for a 120+ unit. They have microswitches that trip the sensor light after so many miles. If the car has had the odometer roll, the mileage will not be the same between the two drums...
wow, thumbs up. that's some good info.
i would also really take a look at the interior. you can definitely tell a 44k mile interior vs a 144k mile interior. unless he took the effort to swap out the seats, cluster gauge, shift knob, shift boot, carpet (clutch and gas heel), etc. there are some good tells.