Well I learned a lot about the Cobra and Corvette parts when I was mocking things up. The Cobra rotors are 0.350" offset parts, while the Corvette rotors are 0.850" parts. It's likely what you have are Corvette rotor cores, drilled with the Explorer hole pattern, my guess.
The stock Explorer rotors are well over 1" offset, close to 1.5" OEM. The farther in they can be, the more wheel clearance you get, and the more wheels that will fit. Some wheels have a lot of meat in the spoke area behind the hub, which is where the caliper sets.
If you make brackets(steel of course), plan the offset to best fit the rotors and calipers you use. It cost no more to alter the dimensions now before anything is made. What you have may be the same part as the XP8 used, and the rotor was chosen to fit that.