The first Coyote was built from a Manta Montage kit car; the second (used later in the series) was built from a DeLorean DMC-12. Reportedly the car was changed because the two men had a difficult time getting in and out of, as well as sitting in, the kit car.
Originally the concept was to have Hardcastle to hunt down all the criminals he prosecuted but were released due to technicalities. In order to keep the A.C.L.U. off of their backs, the producers decided to compromise and have him go after them for current offenses only.