was that tranny in another race car.as fast as it broke its almost like it was already cracked.just a thought.
next time i'd say solid motor mounts and check the body mounts make sure they are not shot.

what would the body mounts have to do with it?

I agree with what John 858 said about checking you body mounts, If they are bad you could have same severe frame movement. The only times I have seen a bellhousing break is because of major torque applied or frame movement, usually from a cracked frame especially a uni body car like your nova. I'd check the frame for cracks too.

Mine were new too. So there was a Vibration? That sounds like a bend driveshaft or out of balance driveshaft. What info do you have on it?
What do the U-Joints look like now? Did it pull the rear one out of the Yoke? How about the front one?

new joints..... the car has a 12 point cage there is no flex

So the driveshaft and U-Joints still look New After the busted case?

yeah. i couldnt tell the bell was broke till i was taking the trans out of the car. or didnt notice it anyway. it doesnt look anywhere on it like any of the brake is old it all looks clean like a fresh brake. i cant find anything that should have caused it to break. the trans was in another car about 4 passes befor i put it in mine. it was fresh clean and everything looked good i didnt see any cracks but it must have been i cant find anything in my setup that should have caused it.

i would still put solid motor mounts on it ,if you got 600hp you will tear those poly mounts up .

I would guess I have about 600HP and I run a stock driveshaft,Yokes,, and mounts. So far no issue's.
I had broke a couple of trannys when I had too much pinion angle, but mine broke at the finishline, both times 2 weeks in a row before I figured it out with help from some good people. :)

not to highjack this thread but WHAT have you done to that truck to make it leave like that,these guys around here can't even come close to you with their s-10's.