9" and 8.8

Dont know if im in the right section im new to the forum but, i havea  84 grand marquis for a derby car with the 8.8 under it and i CANNOT stop breaking axles, i go through atleast 2 a day, my buddy with a 85ish crown vic wagon has the same problem, my question is, what would it take to put a 9" under the car, its not a leaf spring car so i was wondering if the mounting brackets were the same for a 9" as a 8.8 or what i would have to do to get one under the car..

Thanks in advance