I need to replace the (3 pt) seat belts on my 1986 Spider Graduate. I was expecting this to be easier than expected, but it turns out that they are difficult to find. Does anybody have any pointers on this? seatbeltplanet.com has them posted, but then surprisingly mention that "Does not fit convertible" which makes me hesitant. Anybody have some insight on this seemingly trivial issue? Grazie!