8 3/4 guru need your help

Everyone will dis-agree with this. I only know this from experience in my 600 HP,3300 lb Duster, Grinner Brake,Ladder bar and 14 X 32's.If you run the 742 case (not 489), along with a back brace, it will live.The only thing is, as you know they don't make the Pro Gears any more. I always had better luck with the street gears, and ran them any way.Only thing is, about every 2 years, depending on how much you run it,the ring gear will start to chip at the outer edge of the gear.Just check it yearly, and add new ring and pinions.
I also never broke a pinion, but everyone will tell you the tappered one is stronger with crush sleve eliminator. This may be true, but none of us had any problems.
My Valiant had the same combo and weight, but I run a glide, 4th pass last year, I blew my 489 case apart, ring pinion and bearing cap (who knows which broke 1st).It was all new inside also. Richmond gears spool etc.The car came with it, and I just ran it.
I also blew a 489 case apart in my Duster when I 1st built it, it had a SB in it then.
I switched to a 742 case, ran it all year no problem. I now run a Ford 9' just to be safe.