You can go with the B springs... they will work fine on your convertible, although the drop may only be about 0.75 to 1 inch. Is that the drop you are looking for?
Some companies make springs for every Mustang option... different years, different engines, coupe vs. convertible. Sometimes these applications are just for customer clarity... and the spring ratings are just slightly slightly different. Other companies make one spring part number for all models of Mustangs. You can conclude from this, that there is very small differences between springs throughout the years.
Eibach has a specific part number for the V6 convertible. Here is a link
http://www.stangsuspension.com/store...p?idproduct=82
Sincerely,
Sincerely,