You're not going to like it, but you may be SOL. The difference between the brakes on a 97 and a 98 is the mounting bolts for the caliper namely their location. Not really any way to adapt between the two aside from maybe drilling a new mounting hole in the spindle. Honestly I wouldn't even consider that as an option. I'm not even sure that you could get the other bracket if you tried. I'm assuming that you bought Tee-Rev's kit over on TRS. Unless he changed his mind this was the last run of brackets, he only made as many as were paid for, and that's why they asked for the vehicle info (and brake size for the 98 up Rangers).
If you can't find a solution to use this kit some of the 98+ Rangers came with a 12" brakes that can be run by swapping over the spindle. You could go that route and sell off your Cobra brake kit.
Are you sure you can mount your body on the newer frame?