You can quit cruising Hill Street. I found a much easier way to get this son of a bitch car. Near the end of the "Fallen Idol" case, you are confronted by a couple of Guy McAfee's goons. When you leave, they open fire and you have the option to flee or fight.
Kill those sons of bitches and two more that show up. Then steal the car that the first two goons were sitting in when they first accosted you.
It's a Lincoln Zephyr Touring. Bam.