Early in the film when Johnny gives Burke a ride downtown he parks directly behind a 1958 Chevrolet. In the next shot with Burke now out of Johnny's car, the parked car in front is now a 1959 Chevrolet.
As Robert Ryan first drives the souped up Chevy wagon, we hear him grind the gears. Later, as we watch the speedometer climb to 100 MPH, we see the left side of the Powerglide shift quadrant on the steering column. Automatic transmissions don't make gear grinding noises.