Bx-58-c is what I have and that is correct per my ford dealer.
I am not familiar with your particular model year, so I can not confirm that is correct. However, what does your owners manual list as the correct group and size? I do know that Tom (the owner of the '87 Saleen that was at the Savannah show) is looking for a BX58C for his car.
I know on my '86 SVO, Ford does not offer the original group and size, but do offer a service replacement. The service replacement is correct as far as a replacement, but not correct for MCA concours judging.
The easiest way to get to the bottom of this is to contact the judge that judged your car (their number should be on your judging sheet).
Hope this helps.