To add to a few of the previous comments, the 5 (possibly 6)cars built for the show were all "clone" Hemi Cuda convertibles, and no, none of them actually had 426 Hemi's, but all began life as convertibles. A 1971 Hemi Cuda convertible, Lemon Twist Yellow, with a white interior, was Don Johnson's idea for the series. Don Johnson had seen a picture of the one original that exists and decided he wanted to use one just like it in the show (having no idea how rare the car was)
So, after a quick search the #1 car was located in Long Beach California ( it's the car shown in close up still shots that was recently sold on Ebay for over 75K) it began life as a super nice restored 1970 Plum Crazy 4speed 340 convertible. It was used in the pilot show (the series was originally written to be a short mini-series). The camera's didn't pick up the light Lemon Twist Yellow very well so the car was sent off for a "brighter" shade of yellow paint, the color chosen? A non-original color by Sherwin Williams called "Hazard Yellow" (images of yellow parking lot stripes pop into my head
The car was thrashed in the original shooting and it is reported that Don Johnson blew up the original 340 (replacing it with a crate 360 so I've heard). The rest of the cars were a mix of original 1970 and 1971 Barracuda 318 and slant six convertibles in various conditions, the nicer ones used for close shots, the rough ones for stunts and long distance shots. The various cars were cloned to look like 1971 Cuda's with bolt on parts like shaker hoods, painted bumpers (to look like rubber bumpers) 71 grills, gilled fenders, etc. a mix of stock 318's and crate 360's powered them (one had a 440 installed when it was purchased so it was retained and used
after the cosmetic conversion. This is the other car recently sold on ebay for similar money. It was the car most often seen in the drive by shots. The cars used in stunts and jumps were REALLY rough carcasses but they served the purpose
Hope this helps.