Before production began the producers wanted to use a 928. Porsche wouldn't modify the sunroof, make it larger for filming. So they got the Ferrari instead.

I have a few cars. My closest to being "Magnum" related is my Porsche 928. As most fans are aware, originally Magnum was going to borrow a 928. But the Porsche was not a good car for in car scenes. I'm a 1970's kid and teen in the 1980's. So I tend too collect cars from those decades.