what hp can a 742 case 8 3/4 handle

I had a 489 case with 4.30 gears, the car ran 10.20s in a 3400 lb car and got about 40 runs before it broke. I was running the pro gear set (Pro Street). Pro gears from what I was told by a manufacturer will only handle 550 hp. They don't make drag racing gears (Pro Comp) for a 489 case and only make 4.89 gears for the 742. I went to a Dana.