I have broken 2 Dana 70's daily driving my truck with a couple sled pulls and some drag racing. No higher than 350hp. They both just started making noise and when i pulled them apart the pinion was ruined on both of them with a bunch of stress cracks.
I dont have much faith in them myself, but im pretty sure the Smith's truck and several other drag racers are running a Dana 80.
They can be found, just keep your eyes open.
Eric
I never had a problem with either of the Dana 70's i had until they just broke all together. My dana 80 had a spun pinion bearing when i bought it and i had problems with that recently, but I think i have it fixed. At leat for a while.
I thought they should hold what i had no problem, but the 2 i got wouldnt. :bang
Still have the housings, and limited slip units in the shed. maybe a good rebuilt one would have been fine? Both mine had around 200k miles on them.
Eric
If you're drag racing only I wouldn't worry about doing anything to your d70. I'm running low 12s on mine and many are going much faster. If you tractor pull though that's a different story from what i've been told.