89supercharged

morning I am new to the club and have belt question that is driving me crazy.I have a 1989 mustang gt my serpentine belt broke and I am having a hard time finding(you would think it would be simple) the right size.I have a NOVI 2000 installed on it apparently the stock belt should fit not so the car has no a/c I have tried 83.5 belt way too lose 82.5 won't fit is this possible if anyone can help I would really appreciate it ...just wanna drive my car