97- 04 mustang rims again !

Maybe, and I mean maybe, what we should be looking at is the other components. What rotors ?, what spindles ? I'm just guessing, but since you have a fly window, this car is what ? a 1969 ? How was it converted to the big bolt pattern. That said, you may be stuck.
I only avoided the rims your running because of budget, and time constraints. The budget part is - a few of the people on the forum mentioned the bullitt rim was too shallow to accept the factory caps with out spacers, or the need to change rotors to an AR engineering viper set up, or Wilwood. AR Engineering emailed me, and told me their custom caps would fit the bullitt rim, but again only with wheel spacers. They told me, 3/4", but a lot of the fellas here are using 3/8". I'm sure they're safe, some auto cross people are using them too. Reilly MotorSports sells the caps. If you need to contact them, don't be afraid, they're nice people. https://www.reillymotorsports.com/store/help.php?section=contactus&mode=update