I saw an article on a road racing forum once where a guy used Granada or MII spindles on a Cobra kit car and fabricated a set of brakes with used Cobra parts. He had the rotors turned down such that only the hub remained. The Cobra rotor would slip over this. Then he fabbed a bracket to mount the caliper in the proper location. I swear I posted this here once, but I couldn't find it in a search.
I would compare the mounting holes on the Cobra caliper to those used by the various GM and aftermarket suppliers like Wilwood. It may be that someone has already created the caliper bracket that you need or at least one that can be used with some spacers.
But the truth of the matter is...if you are going to drive fast enough to need larger brakes, you probably want to trust your life to a well engineered system from Baer or Wilwood. Baer has several kits that will fit the MII spindle, with both 5x4.5" and 4x4.25" spacing available.
My plan is to machine the 5 lug rotors I have down so just the hubs remain, then use slip-on rotors from a modern setup, probably from a Jeep Cherokee or something similarly heavy, since they have the same 5 lug pattern. As for the brackets, I'm going to fabricate them from steel stock and use the Jeep calipers.