[richsd]

This is a great question. First of all, the only thing that is for certain is that original cars used various methods to bolt down the filler cap and you have named them. Correct Cobra hardware up front (for example on the dash) must certainly be pan head slotted screws. This work was all done in England and a phillips head screw would not be used in England at the time. However, the filler caps were put on by Shelby so other types of screws were used. You will see some pictures of 3042 floating around with hex bolts however another common application for the filler cap was phillips head screws.