Im not sure mate, jus only car ive seen so far with a whaletail is a fox body mustang.

Tho you see them without the kit/spoiler too.

Think I spotted a Mk1/2 vinyl roof Capri last night too.

Was playing it more, and have met Brucie, the steroid muncher who owns the garage.
Man he is PROPERLY funny, I normally skip the cut scenes, but he is properly fucking hillarious, even his emails make me piss.
Reminds me of so many people I know too, almost in tears listening to some of the stuff he says